Video: GCSE Mathematics Foundation Tier Pack 1 • Paper 1 • Question 10

GCSE Mathematics Foundation Tier Pack 1 • Paper 1 • Question 10

01:51

Video Transcript

Calculate three-fifths of 90.

To find three-fifths of a number, we can first find one-fifth of that number by dividing it by five. To divide 90 by five, we can use a short division method. Five goes into nine one time with a remainder of four. Five goes into 48 times with no remainder. So 90 divided by five is equal to 18.

Now to find three-fifths of 90, we need to multiply the value that we’ve calculator for one-fifth by three. So we have 18 multiplied by three. We could do this in a couple of ways. Firstly, we could use a column method. Eight multiplied by three is 24, one multiplied by three is three, and adding the two that we’ve carried gives five. So 18 multiplied by three is 54.

The other way of performing this multiplication would be to use a grid method. We can write 18 as the sum of 10 and eight. 10 multiplied by three is 30 and eight multiplied by three is 24. We can then add these two numbers together using a column addition. And it gives the same answer of 54. Three-fifths of 90 is 54.

We could also check our answer by finding two-fifths of 90. If we think that one-fifth of 90 is equal to 18, then to find two-fifths, we need to multiply by two. Doubling 18 gives 36. Two-fifths of a number and three-fifths of that same number should sum to the total. If we add 36 and 54 together using a column method, we do indeed get 90. So this quick check just gives us a little bit more confidence in our answer.

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