11 Plus Exams Forumhttps://www.elevenplusexams.co.uk/forum/11plus/ Is the answer book wrong?https://www.elevenplusexams.co.uk/forum/11plus/viewtopic.php?f=2&t=61171 Page 1 of 1

 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. 3/8B. 3/5C. 11/15D. 4/5E. 3/15DC 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 = 5/15Ate 2/5 of remaining, so 2/5 x 2/3 = 4/15Altogether 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? Yes1/3 = 5 /15 so she has already eaten 5/15Remaining is 10/152/5 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 correctImagine the pizza had been precut into 15 slicesFirst she eats 1/3 of them ie 5 slices - there are now 10 slices leftThen 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 pizzaYou can see how they choose the "wrong" answers too to catch out the common mistakesA: 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 10/152/5 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 3But 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