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Is the answer book wrong? https://www.elevenplusexams.co.uk/forum/11plus/viewtopic.php?f=2&t=61171 
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Author:  SleepyHead [ Fri Oct 16, 2020 6:44 pm ] 
Post subject:  Is the answer book wrong? 
Alia ate 1/3 of a pizza for lunch. Later she ate 2/5 of the remaining pizza as a snack. How much of the pizza did she eat altogether? A. 3/8 B. 3/5 C. 11/15 D. 4/5 E. 3/15 DC made the answer 3/5 (B) Answer sheet says C 11/15, but I agree with DC! Can anyone explain why it's C please? TIA 
Author:  Tinkers [ Fri Oct 16, 2020 6:47 pm ] 
Post subject:  Re: Is the answer book wrong? 
Answer C is correct. I think youâ€™ve missed that she are 2/5 of the remaining pizza. So you need to work out what 2/5 of 2/3 is, to work out how much is eaten then work out how much is left. 
Author:  SleepyHead [ Fri Oct 16, 2020 6:55 pm ] 
Post subject:  Re: Is the answer book wrong? 
These are our steps: Ate 1/3 = 5/15 Ate 2/5 of remaining, so 2/5 x 2/3 = 4/15 Altogether ate 5/15 + 4/15 = 9/15 = 3/5 Am I missing something 
Author:  mad? [ Fri Oct 16, 2020 7:28 pm ] 
Post subject:  Re: Is the answer book wrong? 
Yes 1/3 = 5 /15 so she has already eaten 5/15 Remaining is 10/15 2/5 of this is 6/15 (x both x 3) so 5/15 + 6/15 = 11/15 
Author:  solimum [ Fri Oct 16, 2020 8:06 pm ] 
Post subject:  Re: Is the answer book wrong? 
I think Sleepyhead is correct Imagine the pizza had been precut into 15 slices First she eats 1/3 of them ie 5 slices  there are now 10 slices left Then she eats 2/5 of the 10 slices ie 4 slices (4/10 and 2/5 are equivalent fractions) She's eaten 9 altogether which is 9/15 or 3/5 of the original pizza You can see how they choose the "wrong" answers too to catch out the common mistakes A: from incorrectly adding 1/3 + 2/5 (adding tops & bottoms of the fractions) C: This would be correct if adding 1/3 +2/5 properly as you would convert both to 15ths 5/15 + 6/15, so without the words "of the remaining pizza" D: ? not sure E: adding 1+2 and multiplying the denominators together 
Author:  mad? [ Fri Oct 16, 2020 8:21 pm ] 
Post subject:  Re: Is the answer book wrong? 
Thanks Solimum. So glad I don't have to to this any more! 
Author:  solimum [ Fri Oct 16, 2020 9:53 pm ] 
Post subject:  Re: Is the answer book wrong? 
One concept which is difficult to grasp with fractions is that the innocuous word "of" means "multiply" so 2/5 OF 2/3 means 2/5 x 2/3 and multiplying fractions is the "easy" one, (2x2)/(5x3) I think where you went astray mad is Quote: Remaining is 10/15 2/5 of this is 6/15 (x both x 3) What you've done there is express 2/5 as its equivalent fraction 6/15 by multiplying top & bottom by 3 But the 15ths here are different from the original 15ths: it's as if you divided the 2/3 of the original pizza into 15 new slices and had 6 of those  those are smaller than the imaginary 15 slices of the original pizza. It would be much easier to explain with real pizza..... 
Author:  mad? [ Sat Oct 17, 2020 5:55 am ] 
Post subject:  Re: Is the answer book wrong? 
Haha or less wine 
Author:  SleepyHead [ Sat Oct 17, 2020 7:18 am ] 
Post subject:  Re: Is the answer book wrong? 
Thanks all 
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