Video: GCSE Mathematics Foundation Tier Pack 3 • Paper 1 • Question 10

GCSE Mathematics Foundation Tier Pack 3 • Paper 1 • Question 10

02:21

Video Transcript

Alex wants to find the answer to 875 divided by 50. He knows that 875 divided by five is equal to 175. He says that 875 divided by 50 equals 1750 because five times 10 is equal to 50 and 175 times 10 is equal to 1750. Is his method correct? If not, describe the error he made.

Well, if we take a look at the question and we look at the information we have, first of all, we have that 875 divided by five is equal to 175. And we got that from the question because it says that he knows that 875 divided by five is equal 175. Now, I’ve written it like this. So it’s as a fraction and I’ve done that so we can actually investigate it a bit further.

So in the question, we’re told that Alex wants to find the answer to 875 divided by 50. Okay, so I’ve written this as a fraction. But what’s this equal to? Well, we can actually rewrite it as 875 over five multiplied by 10 and that’s because 50 is equal to five multiplied by 10.

But can we rewrite it in another way? Well, yes, we can actually rewrite it as 875 over five multiplied by one over 10 or one tenth. And that’s because 875 multiplied by one gives us 875 and five multiplied by 10 gives us our 50 that we had on the denominator.

But we can actually rewrite this again because we can rewrite it as 175 multiplied by one over 10 or one tenth. And that’s because we know that 875 over five is equal to 175 because we were told that earlier. Well, we can clearly see that 175 multiplied by one tenth or one over 10 is not equal to 1750. And that’s because 175 times one over 10 or one tenth is the same as 175 divided by 10 which is equal to 17.5.

So therefore, we can say that Alex is wrong because he has multiplied the left-hand side of this equation by one tenth and the right-hand side of this equation by 10. And these are not equivalent. So therefore, we can say that 875 divided by 50 is not equal to 1750.

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