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Original poster

Maths question

74 replies

Mousewatch · 04/02/2018 15:02

Can anyone tell me what 1/3 of 3/8 is please.

Both DC answered the same, They said that's how the teacher has taught them but the answer on the answer sheet is different.

OP posts:

eddiemairswife · 04/02/2018 17:57

Well, let's hope we get some explanation after the OP has spoken to the teacher.

noblegiraffe · 04/02/2018 18:00

Keep flip change is what you do to divide by a fraction. They have done 1/3 divided by 3/8 where they should have done 1/3 multiplied by 3/8. It's a problem with understanding what the question was asking and they would have probably got it right if the question said 1/3 x 3/8.

GreenTulips · 04/02/2018 18:01

For 3 people to have had 3/8th of a cake there would have had to be 9/8ths to begin with.

dementedpixie · 04/02/2018 18:01

3/8 ÷ 1/3 would be 3/8 x 3/1 = 9/8 = 1 1/8

noblegiraffe · 04/02/2018 18:02

Sorry, I meant they've done 3/8 divided by 1/3

PurpleDaisies · 04/02/2018 18:02

This caught out a load of our kids in the SATS last year too.

As others have said, it’s the “of” that’s confused them. One third of means 1/3 x

The teacher won’t have taught them the maths incorrectly. They haven’t understood how to interpret the problem.

Lweji · 04/02/2018 18:03

They have done 1/3 divided by 3/8 where they should have done 1/3 multiplied by 3/8.

It still doesn't give the 1+ 1/8. It would give 8/9, so either way, it's wrong.

noblegiraffe · 04/02/2018 18:04

Yes Lweji I meant the other way around. Not sure why they changed the order of the fraction.

dementedpixie · 04/02/2018 18:05

They have done 3/8 ÷ 1/3 rather than 1/3 ÷ 3/8

SleepingStandingUp · 04/02/2018 18:06

Lweji · 04/02/2018 18:07

3/8 ÷ 1/3 would be 3/8 x 3/1 = 9/8 = 1 1/8

Oh, I see...
Still, not divided. The teacher wouldn't have found 0,5 of 4/8 by dividing 4/8 by 0,5, hopefully.

noblegiraffe · 04/02/2018 18:09

lweji 3/8 divided by 1/3 gives 1 and 1/8.

So they have switched the order of the fractions, changed the times to a divide. Which is weird.

SleepingStandingUp · 04/02/2018 18:10

Wrote down the wrong numbers....

I got 1 1/8th when I didn't

Lightningbolt82 · 04/02/2018 18:12

If you drew 3/8 , 1/3 would be just one of those pieces (as you would be dividing by 3) so 1/8 is the answer!

PurpleDaisies · 04/02/2018 18:12

They have done 3/8 ÷ 1/3 rather than 1/3 ÷ 3/8

That’s wrong as well.

1/3 / 3/8 = 8/9

noblegiraffe · 04/02/2018 18:15

Yes purple, I meant the other way around. All these fractions are making my eyes go weird!

PurpleDaisies · 04/02/2018 18:16

I know exactly what you mean noble.

I bloody hate doing fractions o the board. It’s so easy to get wrong by failure to copy!

PurpleDaisies · 04/02/2018 18:18

For anyone that has missed it further up the thread, 1/3 of 3/8 means 1/3 x 3/8.

1/3 x 3/8 = 1/8

NotDavidTennant · 04/02/2018 18:34

I think this is a good example of what happens if students see maths as purely being a set of abstract rules. If they'd interpreted '1/3 of' as meaning splitting something into three then finding the correct answer should be straightforward, and at the minimum it would be obvious that an answer larger than 3/8 couldn't possible be correct.

borntobequiet · 04/02/2018 18:42

If they are doing what the teacher told them, and haven't simply misread the question, no wonder I spend so much of my time teaching 18 year olds basic fractions. And decimals. And percentages. And everything else.

Lightningbolt82 · 04/02/2018 18:44

Of means times not divide. 1/3 of 3/8 the same as 1/3 x 3/8 when you multiply anything by a number smaller than 1, your answer gets smaller rather than bigger. If you divide by a number smaller than 1 the answer is larger than the original

HarveySchlumpfenburger · 04/02/2018 19:47

I wouldn’t assume ‘the teacher taught us to do it this way’ means the teacher did show them to do it that way. As a PP said, they could just have applied the method the teacher showed them to the wrong problem.

NotDavidTenant, this is one of those questions that shows those pupils that can do the maths and those that have a genuine understanding/feel for the numbers I reckon.

You don’t actually need the method you’ve been taught to solve it if you know that 1/3 of 3 anything is 1, whether that be apples, cakes, pizzas, tenths, eighths or millionths.

TeenTimesTwo · 04/02/2018 21:15

When she was 8, DD1 came home totally convinced that small yoghurt pots held more than large ones.

Eventually it transpired that they had learned that just because something is taller it doesn't mean it has more capacity. She had 'translated' it to mean it didn't ever have more capacity.

user789653241 · 05/02/2018 08:51

Agree with Rafa. If they are doing 1/3 of 3/8, they must have done questions like 1/3 of 12, 1/4 of 20, etc in the past.
They might be lacking fundamental understanding of fractions, which maybe a problem.

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