Can You Solve These Mental Math Problems?

By: Becky

2+2=

2+2=4. We thought we'd start you off with an easy one.

5x10=

5x10=50. Multiplying by 10 is easy. Whenever you multiply a number by 10, just add a zero to the number.

What is 15% of 30?

15% of 30 is 4.5. When figuring 15%, just take 10%, which is 3, and add half of that, which is 1.5.

21x11=

21x11=231. To multiply a number by 11 in your head, just multiply by 10 (or add a zero to the original number) and add one more of the original number. It looks like this: 21, plus a zero, is 210. Then add 21. The answer is 231.

5x5=

5x5=25. Basic math tables, folks.

360x5=

360x5=1,800. To multiply a number by 5, just divide it in half, then add a zero.

648+250=

648+250=898. For this problem change the 648 to 650 to make it easier to do, then subtract 2 from the result.

What is 10% of 235?

10% of 235 is 23.5. To find 10% of a number, just move the decimal point to the left one place.

200x100=

200x100=20,000. To multiply two numbers with zeroes, just multiply the numbers, then add all the zeroes. It looks like this 2x1=2, then add four zeroes. The answer is 20,000.

1,000-689=

1,000-689=311. To subtract a large number from 1,000, just round the number up to the closest 100, then subtract and add on the remainder. So, think of 100-689 as 1000-700, then add 11.

563x10=

563x10=5,630. To multiply a number by 10, just add a zero.

250x20=

250x20=5,000. To multiply a number by 20, just double the number, then add a zero.

1,250÷10=

1,250 ÷ 10= 125. To divide a number that ends in zero by 10, just remove the zero.

3x4=

3x4=12. We figured you'd welcome an easy one for a change.

22x11=

22x11=242. To multiply a number by 11, just multiply the number by 10, then add the number.

9x9=

9x9=81. It's on the high side of the multiplication table, but you should still know this one by heart.

450x5=

450x5=2,250. To multiply a number by 5, just divide the number in half, then add a zero.

4,200+500=

4,200+500=4,700. To add thousands, just think of them as hundreds. So, 42 hundreds plus 5 hundreds, is 42+5, which is 47 hundreds, or 4,700.

200+300+40=

200+300+40=540. Think of this as 2 hundreds plus 3 hundreds plus 40.

69+18=

69+18=87. Think of this as 70+18=88, then subtract 1 to get 87.

10x10=

10x10=100. Break time.

56x100=

56x100=5,600. To multiply any number by 100, just add two zeroes to the number.

369÷10=

369 ÷ 10=36.9. To divide any number by 10, just move the decimal to the left one place.

240x2=

240x2=480. To multiply a number by two, just double it, or add it to itself.

70+20+80=

70+20+80=170. Since we can easily see that 20+80=100, do that part of the problem first, then add 70 to get the answer of 170.

25+38+75=

25+38+75=138. We can easily see that 25+75=100, so lets rearrange the problem so that it's easier.

396÷100=

396÷100=3.96. To divide any number by 100, just move the decimal to the left two places.

15-7=

15-7=8. It's easier to think of this as an addition problem. What do you need to add to 7 to reach 15?

53+56=

53+56=109. Think of this as 50+50+3+6=109. It's about breaking numbers into easier to digest pieces.

7x300=

7x300=2100. Just multiply 7x3, then add two zeroes.

6x49=

6x49=294. Think of this as 6x50=300, then subtract 6 (because you're dealing with 49, not 50.)

8x15=

8x15=120. Some numbers are easier to multiply in your head if you change them. For this one, cut one in half, then double the other to make it easier to manage. Half of 8 is 4, and double 15 is 30, so 4x30=120.

56÷8=

56 ÷ 8=7. Think of this as multiplication instead. What times 8 equals 56?

56÷100=

56÷100=0.56. To divide by 100, just move the decimal to the left two places. In this case, that makes the answer less than one.

5+5=

5+5=10. We made it easy-peasy for you. We figured your brain might be tired.

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About This Quiz

Were you a mental math athlete, or mathlete, in school? Has it been a while since you flexed your mental math muscles? If you think you've still got what it takes to ace a mental math challenge, take this quiz to find out how much you really remember!

We know that you've probably heard of the national spelling bee, but did you know that there are similar competitions at various levels (city, state, regional, national, etc.) for kids who excel in math? Well, it's true. Just in case you weren't a nerd in school, or you didn't hang out with nerds, there are actual competitions where students go to compete with other math geniuses. OK, so most of them aren't geniuses, but they certainly have mastered some pretty cool ways to perform mathematical equations in their heads. These kids are called "mathletes" these days, and they gather regularly to practice those snazzy mental calculations and to compete against one another before heading off to a regional, or even national, competition.

So, if you were one of those nerds, we've got a quiz to bring back some, hopefully good, memories.  If not, we've sneaked some simple tricks into this quiz to help you learn how solve these equations without a calculator.

Let's find out how much mental math power you still have!

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