Video: KS2-M17 • Paper 1 • Question 12

62/100 − 38/100 = _.


Video Transcript

Sixty-two hundredths take away thirty-eight hundredths equals what?

We know that we can subtract these fractions because they have the same denominator. Remember that the denominator or the bottom number in a fraction shows us the number of equal parts that the whole has been split into. So if we think of this square is representing one whole, a denominator of 100 means that our whole has been split into 100 equal parts. Each of these smaller squares is worth one hundredth.

Remember also that the numerator or the top number in a fraction is the number of those parts that we’re dealing with. So for example, in the first fraction here, the numerator is 62. So our subtraction starts with sixty-two hundredths.

As we’ve already mentioned, because the two denominators are the same, this means that we can subtract these two fractions easily. We start off with a number of hundreds and we subtract the smaller number of hundreds. So we know that our answer is going to be a number of hundredths, whatever’s left. the denominator in our answer then is going to be 100.

What about the numerator? How many hundredths are we left with? Well, if we start with sixty-two hundredths and then subtract thirty-eight hundredths, the answer is going to be equivalent to 62 minus 38. What quick method could we use to find the answer to 62 minus 38?

One mental method we could use to find the answer is to start with 62 and then to partition 38 into tens and ones. So subtract 30 and then subtract eight. Another method might be to start with 38 and to find the difference between 38 and 62. We could do this by counting on.

A third method is to spot that the number 38 is very close to the number 40 and it’s easy to take away 40 from another number. This is an interesting and a quick strategy we can use. So let’s do that now. Start with 62. And because 38 is so close to 40, we’ll subtract 40 instead. 62 take away 40 equals 22.

Now although subtracting 40 was very quick, it’s not what we wanted to subtract. We wanted to subtract 38. So we’ve taken away two more than we needed to. So let’s add two onto our answer. 22 plus two equals 24. So 62 take away 38 equals 24. And so, we’ve found our numerator, which is 24. Sixty-two hundredths take away thirty-eight hundredths leaves us with twenty-four hundredths.

Interestingly, we could also use our knowledge of decimals to find the same answer, but express it in a different way. Sixty-two hundredths can be written as 0.62. And we can write thirty-eight hundredths as 0.38. Then, we can use our knowledge of subtracting 38 from 62 to help us subtract 0.38 from 0.62. The answer will be 0.24 or twenty-four hundredths. Both of these answers are equivalent. Use whichever method you’re most comfortable with.

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