This blog is managed by Song Hock Chye, author of Improve Your Thinking Skills in Maths (P1-P3 series), which is published and distributed by EPH.

Friday, January 16, 2009

Tao Nan School P5 SA2 2007 Math Q41

Lily and Kumar had an equal number of marbles. After a game, Lily lost 20 of her marbles. Lily then had 1/3 as many marbles as Kumar. How many marbles did each of them had at first?

Solution



2 units ----- 20
1 unit ----- 20 divided by 2 = 10
3 units ----- 3 x 10 = 30

Answer: They had 30 marbles each at first.

10 comments:

Anonymous said...

Information given in the question is not complete.

Excel Eduservice said...

Corrected the missing portion. Thanks.

Fellow said...

Hello! Just happen to enter into this website to find out how PSLE aggregate is calculated. Found so much useful info here. Thanks so much!
Sorry but I think the answer of 30 marbles each of them had at first is incorrect. The difference of 20 in the model is wrong to begin with. The correct answer should be 40.

Tilted Earth said...

Hi

Each one of them has 30 marbles at first is the correct answer.

Sanny said...

Hey. The correct answer should be 40. Please check the steps before posting your solution.

Excel Eduservice said...

To Sanny,

Your answer is wrong. The question states that Lily lost 20 of her marbles. That means BEFORE she lost it, she had those twenty marbles with her and those twenty marbles she lost, plus the ones she did not lose, were equal to the number of marbles Kumar has.

So AFTER she lost 20 of her marbles, she only has 1/3 of Kumar’s. The difference of 2 units is therefore 20 marbles.

Your mistake is to assume that Lily LOST HER MARBLES TO Kumar. The question did not state that. Because you assume that, you make the mistake that the 2 units difference between Lily and Kumar after Lily lost it, is therefore 2 units --- 40.

Students are asked to read the questions carefully during exams. It is quite a waste if you lose marks because of careless mistakes.

Sanny said...

That's tricky. Thanks for the explanation!

Anonymous said...

This question can be solved easily using Unit Transfer Method. Before and After concept, SIngle unchanged quantities as follows:


Lily Kumar
Before 1x3=3 1x3=3
Change -20
After 1 3

2u = 20
1u = 10
3u=30

This bookmcan be bought at www.mathsheuristics.com

SoHolyTsunami said...

Hello, Somebody here..



the answer is 40 because after she lost 20 marbles she got 3units but if she did not lose 20 she will have 2units So

3units - 2units = 1units
1units->20
2units->20 X 2 = 40

SoHolyTsunami said...

Hello, Somebody here..



the answer is 40 because after she lost 20 marbles she got 3units but if she did not lose 20 she will have 2units So

3units - 2units = 1units
1units->20
2units->20 X 2 = 40