Math is weird. Honestly, most of us haven't thought about long division since we were sitting in a cramped plastic chair in the fourth grade, desperately staring at the clock and hoping for recess. But then you’re trying to split a $87 restaurant bill five ways, or you’re measuring out 87 inches of fabric for a DIY project and realize you need five equal strips, and suddenly, the brain fog hits. 87 divided by 5 isn't one of those clean, easy equations like 100 divided by 4. It’s got a remainder. It’s got a decimal. It’s got a little bit of attitude.
The answer is 17.4.
Simple, right? Maybe. But the way we get there—and why our brains struggle with "7s" and "5s" together—is actually pretty fascinating.
The Core Breakdown of 87 Divided by 5
If you want the quick and dirty math, here it is. You take 87. You see how many times 5 goes into it. 5 goes into 80 exactly 16 times. Then you have 7 left over. 5 goes into 7 once, with 2 left over. So you’re looking at 17 with a remainder of 2.
In decimal form, that remainder of 2 becomes .4 because 2 is two-fifths of five.
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Why does this feel harder than it should? It's because the number 87 is "clunky." In mathematics, numbers like 87 are what some teachers call "fake primes." It looks like it should be prime—it feels lonely and indivisible—but it’s actually 3 times 29. When you try to jam a 5 into it, it doesn't fit the base-10 patterns our brains love. We love 5s. 5, 10, 15, 20... they're rhythmic. 87 breaks that rhythm. It's a jagged edge in a smooth world.
Breaking it down for different scenarios
Think about money. If you have $87 and you're splitting it between five friends, everyone doesn't just get 17 bucks. They get $17.40. That 40 cents matters. If you’re a server at a restaurant and five people leave an $87 tip (lucky you), and you have to split that with the back-of-house staff, you’re counting out those quarters and dimes.
- The Long Division Method: You put the 5 outside the bracket and the 87 inside. 5 goes into 8 once. Subtract 5 from 8 to get 3. Bring down the 7. Now you have 37. 5 goes into 37 seven times (since 5 times 7 is 35). Subtract 35 from 37 and you have 2. Add a decimal and a zero. 5 goes into 20 four times. Boom. 17.4.
- The "Double and Drop" Trick: This is a mental math shortcut experts use. To divide any number by 5, just double the number and move the decimal point one spot to the left. Double 87 is 174. Move the decimal? 17.4. It works every single time. It's basically magic.
Real-World Math: When 17.4 Actually Matters
We aren't just doing this for fun. Or maybe some of you are, which is cool too. But usually, 87 divided by 5 pops up in construction, cooking, or budgeting.
Imagine you are a carpenter. You have a board that is 87 centimeters long. You need to cut five equal pieces for a small shelving unit. If you cut them at 17 centimeters, you’re going to have a weird leftover scrap of 2 centimeters. That’s nearly an inch. It’ll ruin the alignment. You need exactly 17.4cm. But wait—did you account for the "kerf"? That’s the width of the saw blade. If your blade is 2mm thick, your 17.4cm cuts are actually going to result in a much shorter final piece. Real-world math is messy.
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In the world of fitness, maybe you're tracking your macros. You've got 87 grams of fat to distribute over five meals. That’s 17.4 grams per meal. If you’re a competitive bodybuilder, that .4 matters for your caloric intake. If you're just a normal person trying to eat a salad? It’s basically 17 grams and a tiny bit of dressing.
The Psychology of the Number 87
There is a reason why 87 feels "off." Number theory suggests we find comfort in symmetry. 87 is odd. 5 is odd. When you divide an odd by an odd, you don't always get a clean result, and our brains are hardwired to look for "anchors."
Research from the University of Oxford on mathematical cognition suggests that humans process numbers relative to their proximity to "landmarks" like 10, 50, or 100. 87 is just far enough away from 90 to feel like it requires extra effort. It’s in no-man's land. It’s the "Sunday night" of numbers—it’s not quite the weekend (the 80s), but it’s staring down the barrel of Monday (90).
Common Mistakes People Make
People often guess 15 or 16. Why? Because they know 5 times 20 is 100, and they try to work backward. They think, "Well, 87 is about 15 less than 100, so maybe the answer is 17?" They get lucky with the guess, but the logic is shaky.
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Another mistake is forgetting the decimal. 17 with a remainder of 2 is fine for a third-grade worksheet, but in a bank or a lab, 17.2 is wrong. Remember, a remainder of 2 out of 5 is 40%, or .4. If you write 17.2, you’ve just failed your chemistry exam.
Why Calculators Might Sometimes Confuse You
If you use a very old or specific type of scientific calculator, and you aren't careful with your settings, you might see 17.40000000. It’s the same thing. But in significant figures—something scientists like Neil deGrasse Tyson talk about often—the precision of your "87" and your "5" dictates how you should report that 17.4. If you only measured the 87 to the nearest whole number, saying "17.4" implies a level of precision you might not actually have.
How to Memorize This
You probably don't need to memorize what 87 divided by 5 is for the rest of your life. But if you want to be "that guy" at trivia night or just sharpen your brain, remember the 17.4 figure by associating it with 1774—the year of the first Continental Congress in the U.S. (well, close enough). Or just remember the "double and drop" rule.
87 doubled is 174.
17.4.
It’s the most efficient way to handle any division by 5.
Actionable Next Steps
- Practice the Double and Drop: Try it with 42 divided by 5. Double 42 (84), move decimal (8.4). Try it with 120. Double (240), move decimal (24). It’s a literal superpower.
- Check Your Measurements: If you’re doing home DIY, always use decimals or fractions (17 2/5) rather than "remainders."
- Think in Percentages: Realize that .4 is 40%. It helps visualize the "leftover" part of the number much more clearly than just a "remainder of 2."
Math doesn't have to be a nightmare. It's just a set of rules for the universe. Even a "clunky" number like 87 has to play by those rules. 17.4 might not be a "pretty" number, but it’s the truth, and in math, the truth is all that matters.