## Q&A - PSLE Math

### Re: Nanyang 2011 ca1 question

u are posting in the wrong thread - there's a thread Q&A for Px Maths for each level...

- edlynnalexander
- OrangeBelt
**Posts:**95**Joined:**Sat May 05,**Total Likes:**1

### Re: Q&A - PSLE Math

need some help in this question.

there were 640 stamps in 2 boxes altogether.

1/3 of the stamps are transferred from box A to box B.

Then 1/3 of the stamps in box B are transferred to box A.

As a result, the number of stamps in box B is 1/3 of the number of the stamps in box A.

Find the number of stamps in box A at first

there were 640 stamps in 2 boxes altogether.

1/3 of the stamps are transferred from box A to box B.

Then 1/3 of the stamps in box B are transferred to box A.

As a result, the number of stamps in box B is 1/3 of the number of the stamps in box A.

Find the number of stamps in box A at first

### Re: Q&A - PSLE Math

May I know how do u assume the 5/5 units?edlynnalexander wrote:ttlkbs wrote:

Pls help! Thank-you!

- alfretztay
- KiasuGrandMaster
**Posts:**1199**Joined:**Sun Sep 12,**Total Likes:**5

### Re: Q&A - PSLE Math

I would solve the above problem as follows :ozora wrote:May I know how do u assume the 5/5 units?edlynnalexander wrote:ttlkbs wrote:

Pls help! Thank-you!

**:**

*At first*A -> 10u + 200

J -> 10u

**:**

*After A gives 60% to J*A -> 4u + 80

J -> 10u + 6u + 120 = 16u + 120

**:**

*After J gives 25% to A*A -> 4u + 80 + 4u + 30 = 8u + 110

J -> 12u + 90

12u + 90 – (8u + 110) = 200

4u -> 220

1u -> 55

55 x 10 + 200 = 750

Ans :

*750 books.*- alfretztay
- KiasuGrandMaster
**Posts:**1199**Joined:**Sun Sep 12,**Total Likes:**5

### Re: Q&A - PSLE Math

I would solve the above problem as follows :ozora wrote:need some help in this question.

there were 640 stamps in 2 boxes altogether.

1/3 of the stamps are transferred from box A to box B.

Then 1/3 of the stamps in box B are transferred to box A.

As a result, the number of stamps in box B is 1/3 of the number of the stamps in box A.

Find the number of stamps in box A at first

640/4 = 160

Working backwards,

**:**

*A*

*B*480 : 160

-80 … +80

—– … —–

400 … 240

+200 … -200

—– … ——

600 … 40

…

Ans : 600 stamps.

- alfretztay
- KiasuGrandMaster
**Posts:**1199**Joined:**Sun Sep 12,**Total Likes:**5

### Re: Q&A - PSLE Math

I would solve the above question as follows :ttlkbs wrote:

Pls help!

5(B + C) = 4A

4A = 5B + 5C

8A = 10B + 10C

20A = 25B + 25C

A/6 = B/5 + C/3

5A = 6B + 10C

20A = 24B + 40C

3A = 4B = 60C

1A -> 20C

1B -> 15C

area of A : B : C -> 20 : 15 : 1

Ans : 20 : 15 : 1

### Re: Q&A - PSLE Math

thanks. and thanks for the previous question as wellalfretztay wrote:I would solve the above problem as follows :ozora wrote:need some help in this question.

there were 640 stamps in 2 boxes altogether.

1/3 of the stamps are transferred from box A to box B.

Then 1/3 of the stamps in box B are transferred to box A.

As a result, the number of stamps in box B is 1/3 of the number of the stamps in box A.

Find the number of stamps in box A at first

640/4 = 160

Working backwards,

:AB

480 : 160

-80 … +80

—– … —–

400 … 240

+200 … -200

—– … ——

600 … 40

…

Ans : 600 stamps.

### Re: Q&A - PSLE Math

alfretztay wrote:I would solve the above question as follows :ttlkbs wrote:

Pls help!

5(B + C) = 4A

4A = 5B + 5C

8A = 10B + 10C

20A = 25B + 25C

A/6 = B/5 + C/3

5A = 6B + 10C

20A = 24B + 40C

3A = 4B = 60C

1A -> 20C

1B -> 15C

area of A : B : C -> 20 : 15 : 1

Ans : 20 : 15 : 1

### Re: Q&A - PSLE Math

I would solve the above problem as follows :alfretztay wrote:May I know how do u assume the 5/5 units?edlynnalexander wrote:ttlkbs wrote:

Pls help! Thank-you!

**:**

*At first*A -> 10u + 200

J -> 10u

**:**

*After A gives 60% to J*A -> 4u + 80

J -> 10u + 6u + 120 = 16u + 120

**:**

*After J gives 25% to A*A -> 4u + 80 + 4u + 30 = 8u + 110

J -> 12u + 90

12u + 90 – (8u + 110) = 200

4u -> 220

1u -> 55

55 x 10 + 200 = 750

Ans :

**[/quote]**

*750 books.*Thank-you to both Edlynnalexander and Alfretztay.

The correct answer is 750.