This is directed especially at young people, who need a little help figuring out how to process the extraordinary numbers that are mentioned in the Bible, especially in the Old Testament. I'm not going to do a big long scholarly thing with passage citations, but just give you some tips to consider.
First of all, the Bible is the Word of God, given to various humans, usually of the prophetic, priesthood or judges office. The Holy Spirit ensures that the concepts of God, which cannot be properly understood by humans, are translated into an acceptable form when they are put into human speech and writing, thus becoming part of the Holy Scriptures.
So you can, and indeed if you have faith you *must* believe all that is in the Bible, for it is true, and it is the inspired Word of God.
However, in the Catholic Church it is well understood that there are times that numbers are used very precisely, while other times they are used symbolically, and that still other times numbers are used as a kind of "secular slang," while still representing sacred concepts. It is the latter I wish to point out and explain to you, after first a few words are the first two uses of numbers.
Early in Genesis, when Adam and Eve have had their fall, and humans must toil to make their own living, God states that the maximum life span of humans will be one hundred and twenty years. So in the earliest scripture humans obviously have an understanding that God has set a biological limit on human lifespan, and it is obvious that God shared this information with them since humans had no way of having biological population observations and studies of how long humans could live, reaching the precisely accurate number of one hundred and twenty, all on their own! Look through Wikipedia and read about those of great longevity and sure enough, even under modern ideal circumstances, one or two humans have reached 122 and 121, and the rest all fall right around or before 120.
So, when you read that some of the elders lived to an extra ordinary length of years, a few many centuries, you have to believe that and cannot say, "Oh, well, they weren't precise about measuring age back then." They were precise because in the earliest scriptures they were told by God (through Moses) that this is the span of humans. Thus, people would have not just "made up" great ages for some of the ancients just to be artistic, out of ignorance, or some inflated desire to exaggerate. This is one of the great mysteries of God, but is a foundation of faith in God, that those few within whom the pure spirit of God resides, they can defy death for centuries, if that is God's will. So when it comes to matters of individual genealogies, you can have confidence in the precision of the Bible authors.
When it comes to the amount of time that God utilizes to either perform a deed or to prophesy about future events, you must trust in God and recognize that God is being symbolic, since humans are unable to understand God's sense of "time" since he is of himself totally self contained and timeless. The classic example is the seven days of creation with the day of rest. God chose to explain creation to Moses using the concept of "days," meaning equal spans of time. However, you must understand, and it is Catholic doctrine, that humans have no way of knowing what a "day" means to God, and that one day to God may be two billion years each in human's time, for all humans know. When God selects to use a human concept such as the seven days of creation and day of rest, he is obviously doing so for a reason. God will, for example, put the "timing" of his deeds in order to match human cycles of activity, in order to reinforce and guide them in their modeling of their actions after God's example. Thus God "wanted" humans to have a day per week in order to rest, not be forced to work, and also to worship and have time for prayerful contemplation and activities. See what I mean? God wouldn't want to tell Moses that it took 14 billion years to create the universe as it stands today simply because the whole point of science is science, and of scripture is of scripture, and so the book of scripture is not a science textbook. It is a book of sacred history, the secular events that take place within humanity's sacred history, and also of God's commandments and expectations, plus his loving guidance. Thus like a father teaches a young son, God will say "soon" to mean "human soon," or "later" to mean "human later," or a week to mean a human week, so that the little one can understand the general outline of what God is demonstrating and exhorting humans to do. This is what a "symbolic" use of numbers means. This does not mean that they are "sacred numbers" in the sense of "magic numbers." This is a modern exaggeration and error that is dangerous and misleading. The Bible does have what they call "sacred numbers" but it is for the reason I just explained, that God wants humans to model themselves after certain quantities for certain actions, but not because there is a "wave the magic wand" quantity about the number.
As another example of this, look at the number forty. It is a sacred number in the sense that it models a concept for humans that is godly in intention. For example, Jesus fasted for forty days in the desert. It's not that the number forty is "magical," as if for example, there is some "magic spell" in whether Jesus fasted for 4o days instead of 39 days or 41 days. The significance of the number of days that Jesus fasted is that it is well over a month, nearly a month and half. This means that is it an extreme fast that could only have been sustained by total faith and the power of the Holy Spirit. We know that humans can, in theory, survive without food for two to three weeks. When one takes it to well over the average survivable time, one is putting oneself in God's hands through the power of one's faith. Thus Jesus fasted for forty days, not as acknowledgement of some sort of numerology, but to use a span that is a fundamental test of and lesson for all of his faith and sustenance by the Holy Spirit.
Many make a linkage between the "forty" years in the desert of the Israelites during Exodus and Jesus fasting for forty days. See, this is the danger of modern thinking. It is fine, and even correct, to notice that forty has a symbolic nuance and meaning, but one must still be careful not to "empower" the number with "magic" meaning, but to understand its symbolic significance within each context of occurrence! Remember that life was harsh and short in those days. An adult was viewed as being an elder in their thirties to forties. While many Biblical figures lived good long average lives, to their seventies and eighties, the vast majority of people (just as those in the lesser developed parts of the world to this very time) lived only to their thirties, forties and fifties. There is nothing magical, therefore, about the forty years in the desert. The Bible explains that this was to shed the Israelites of the generation that had been born into slavery and knew only a slave's mindset. A "generation" is defined as thirty years, both in the Bible and in modern population studies. So the symbolic meaning of the actual amount of time (since they did indeed spend forty years in the desert) is that just like the fasting in the desert, it is a stretch beyond average survivability. Jesus fasted for forty days because it is an amount that can only be borne through faith and the Holy Spirit. The Israelites wandered in the desert for forty years so that one generation could pass away through natural causes and what was "old age" in those times, and the new generation that were not slaves takes their places. Thus forty occurs as an exact number, and is to be believed, but it is to be understood that it is exact only because it reflects a greater reality of God's intention within each individual circumstance. So we have two examples of symbolic numbers, the seven of the days of creation and rest (which are not exact in the sense of human days, but are exact in that they are models for the human work and worship week, plus reflect some insight into God's cycle of creation, foreshadowing when humans would understand the science of physics, geology and biology) and the forty days of fasting, along with the forty days of Exodus wandering, which are exact in their correctness, but are exact because they symbolize a length of time that is "needed" to achieve a purpose.
OK, the third thing that you need to watch for, then, are numbers that are secular slang that are used in God approved Scripture such as the Bible. One example would be when you read that "ten thousand were slain" or "ten thousand died" in punishment, or due to disease or so forth. Obviously, you must compare how precise that Biblical authors are in some areas (such as the ages of the patriarchs, and the hour and day that sacred events occurred) with wondering, what are the odds that exactly ten thousand people would have fallen in battle, and did they count? Obviously not. I've thought of an example that you can relate to in order to explain how to "believe" the accuracy of the Bible, yet interpret those numbers the way that you should.
When I was growing up a popular slang expression was using "a ton" to refer to an awful lot of something. For example, in school we would say we were assigned "a ton" of homework. Now, obviously we were not assigned two thousand pounds of homework. And if someone in the future read one of my school days letters from that time, they'd be making an error to believe that two thousand pounds of homework was assigned to me and my classmates and they would be making an error to think that two thousand was a "magic number" in the American school system. For decades using the expression "a ton" to describe just about everything (including, "I got a pizza with a ton of toppings") was an extremely common expression in all areas of life, from the momentous to the petty and mundane. No one meant that what they were saying had anything to do with an actual ton or that it was significant to imply two thousand pounds! For example, I make "a ton of typos" if I do not have a real time spell checker, but that does not mean I make two thousand pounds of typos in my virtual word processor pages!! Hmm.
Likewise, people who did not read or write but had a vivid and sophisticated speech used certain quantities to imply grandness or smallness of scale and, just as I pointed out above, significance within the specific context. For example, think of what ten thousand people meant to the Israelites. That would be the population of a very significant sized city, or the entire population of a heathen tribe, or all the settlements and their accompanying population within a significant and sizable geographic area. So when Bible authors recorded that "ten thousand died," they were using secular slang to imply one of the concepts as I described above, such as total devastation of a huge city, or the equivalent of wiping out an entire generation of men, or the loss of everyone in a vast territory. There is nothing magic about the number itself. People who become obsessed with, for example, the "ten" of the "ten thousand" are like those who think that when I say my pizza had a ton of toppings that I meant there were two toppings, each of one thousand pounds, since two thousand pounds starts with "two!" LOL. When people were less modern and less smarty pants, right up to the most recent two generations, they knew that without explaining. They could read the Bible (or listen to it in church if they could not read) and when they heard "ten thousand died," they'd never look for a magic or hidden meaning in the number. They would "get it," just as the actual dwellers of Biblical times, that it was "a lot" that died, with a particular meaning and level of destruction.
It's like if you read in today's papers that "an entire battalion was wiped out by terrorists in battle." You'd be horrified and have a sense of magnitude without most people having a clue as to how many soldiers are in an actual battalion.
So when you read numbers like that you miss the point of what the contemporary Biblical scribe is telling you if you either 1) assign a heavy handed "magical" meaning to it or 2) do not understand what a quantity of that size like that "meant" in "those days." Like I said, using a term such as "ten thousand died" is making a secular slang statement that implies a huge level of destruction that has implications of a city, a tribe, or a generation being impacted and gone.
You can see now why some Christians that are outside of the Catholic Church have made a real mess of trying to assign dates, quantities and times to Biblical prophesy, especially in the visions of Daniel, Ezekiel, and in the Book of Revelations. They are unable to discern that God is using language to help humans grasp the dimensions of what God is doing and saying. God does not expect nor should people presume upon themselves to assign literal dates, places, and quantities that God does not choose to spell out in such a way. Thus God inspires in the Bible authors, including St. John "the Revelator," numbers that convey a message or scale of destruction or dimension so that people get the general drift of what is to come, but not to become micromanaging false prophets that use calculators and spreadsheets to think they know "when" God will do "what." They need to cool their jet skis and calm down and read the usage numbers in the reasonable way that I explained, going back to the Old Testament, and discern that ultimately numbers are ways to convey both literal quantities and "dimension" or "scale" of impact, such as I explained regarding the "ten thousand" having died and what it would mean if we said "a battalion" or "a ton" in the news today. It's scale and gravity, in those cases, not a magical significance of the numbers itself.
I really hope that you find this helpful. I think it should, because those who grind away at trying to extract some sort of numerology dictatorship from the use of numbers in the Bible are doing themselves a real disservice in understanding, and adding a great deal of work, worry and headache that is unproductive an, in fact, sadly erroneous. The Bible should be read with freedom, liberation and joy, that comes from proper context and trust in God, and not from being dragged into a depressive pit of wresting "secrets," "magic," and "meaning" and thus missing the true meaning of the holy scripture in all that painful digging and distortion.