Multiply a one-digit number by 90.
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Grade 3 · Multiplying by Multiples of 10 · question 1 of 3
0 of 12
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2 × 90 =
0:00 of 3:25
90 is 9 tens.
A number times 90 is that number times 9 tens.
5 × 10 = 50: 5 jumps of 10 from 0 land on 50: 10, 20, 30, 40, 50. Jumps of 90 work the same way: 2 jumps of 90 land on 180.
Each jump of 10 is 1 ten, so 5 jumps of 10 is 5 tens: 50.
3 × 10 = 30: 3 jumps of 10. And 2 × 90 = 180: 2 jumps of 90.
Bigger jumps work the same way: count the jumps, read the landing. 90 is 9 tens, so a jump of 90 is 9 tens at once.
The number of jumps times the size of a jump is where you land.
Adding instead of jumping: 5 and 10 make 15.
5 jumps of 10: 10, 20, 30, 40, 50. So 5 × 10 = 50.
9 × 90 = ___ — 810. 9 jumps of 90: 90, 180, 270, 360, 450, 540, 630, 720, 810. So 9 × 90 = 810.
What is 3 times 90? Let's use a trick with tens to solve it fast.
Ninety is the same as 9 tens, because 9 times 10 equals 90.
Here are 9 groups of 10 — that's what 90 really means.
So we can rewrite 3 times 90 as 3 times 9, times 10.
First, multiply the easy fact: 3 times 9 equals 27.
Now multiply 27 by 10. Multiplying by 10 just means adding a zero, so 27 times 10 is 270.
So 3 times 90 equals 270! Once you know your 9s facts, every times-90 problem is just one more step.
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