Can You Solve These Mental Math Problems?

By: Becky

Can You Solve These Mental Math Problems?
Image: shutterstock

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!

5x10=
5
10
50
5x10=50. Multiplying by 10 is easy. Whenever you multiply a number by 10, just add a zero to the number.
1,000

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5x5=
5
25
5x5=25. Basic math tables, folks.
100
15

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648+250=
999
768
898
648+250=898. For this problem change the 648 to 650 to make it easier to do, then subtract 2 from the result.
1,013

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2+2=
2
4
2+2=4. We thought we'd start you off with an easy one.
8
16

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563x10=
5.63
.563
5,630
563x10=5,630. To multiply a number by 10, just add a zero.
563

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1,000-689=
498
311
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.
109
231

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3x4=
6
12
3x4=12. We figured you'd welcome an easy one for a change.
7
9

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What is 10% of 235?
23.5
10% of 235 is 23.5. To find 10% of a number, just move the decimal point to the left one place.
2.35
.0235
1.7

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200+300+40=
54
230
540
200+300+40=540. Think of this as 2 hundreds plus 3 hundreds plus 40.
360

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250x20=
1,250
5,000
250x20=5,000. To multiply a number by 20, just double the number, then add a zero.
500
7,500

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What is 15% of 30?
4.5
15% of 30 is 4.5. When figuring 15%, just take 10%, which is 3, and add half of that, which is 1.5.
300
15
2

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450x5=
4.50
2,250
450x5=2,250. To multiply a number by 5, just divide the number in half, then add a zero.
950
1,450

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69+18=
78
87
69+18=87. Think of this as 70+18=88, then subtract 1 to get 87.
51
102

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21x11=
210
231
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.
111
211

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4,200+500=
3,700
470
4,700
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.
970

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9x9=
18
56
81
9x9=81. It's on the high side of the multiplication table, but you should still know this one by heart.
72

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10x10=
1,000
1,100
100
10x10=100. Break time.
110

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70+20+80=
170
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.
100
80
150

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1,250÷10=
12.50
125
1,250 ÷ 10= 125. To divide a number that ends in zero by 10, just remove the zero.
12,500
250

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369÷10=
3.69
36.9
369 ÷ 10=36.9. To divide any number by 10, just move the decimal to the left one place.
3690
3.069

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56x100=
5,600
56x100=5,600. To multiply any number by 100, just add two zeroes to the number.
560
56
5,560

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240x2=
240
120
480
240x2=480. To multiply a number by two, just double it, or add it to itself.
460

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53+56=
59
82
109
53+56=109. Think of this as 50+50+3+6=109. It's about breaking numbers into easier to digest pieces.
111

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25+38+75=
96
171
138
25+38+75=138. We can easily see that 25+75=100, so lets rearrange the problem so that it's easier.
143

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15-7=
7
8
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?
3
9

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6x49=
398
294
6x49=294. Think of this as 6x50=300, then subtract 6 (because you're dealing with 49, not 50.)
789
463

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8x15=
104
53
120
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.
115

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22x11=
141
242
22x11=242. To multiply a number by 11, just multiply the number by 10, then add the number.
1063
222

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56÷8=
7
56 ÷ 8=7. Think of this as multiplication instead. What times 8 equals 56?
8
9
6

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5+5=
10
5+5=10. We made it easy-peasy for you. We figured your brain might be tired.
100
1000
15

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7x300=
21.00
210
2,100
7x300=2100. Just multiply 7x3, then add two zeroes.
2,700

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200x100=
200
2,000
20,000
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.
2,100

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56÷100=
0.56
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.
5.6
560
0.056

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396÷100=
39.6
3960
3.96
396÷100=3.96. To divide any number by 100, just move the decimal to the left two places.
0.396

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360x5=
1,600
185
1,800
360x5=1,800. To multiply a number by 5, just divide it in half, then add a zero.
750

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You Got:
/35

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