Q&A - PSLE Math

[tianzhu]

Beikiasu:

asked by mummy.

Hi

120%:100%

120:100

6:5

Best wishes

[speedmaths.012624com]

Musicstar:

Please help me to solve these questions. Thank you.


1) Tank A , B and C contained some water. 1/3 of the water in Tank A was transferred to Tank B. 1/4 of the water in Tank B was then transferred to Tank C . Lastly, 1/5 of the water in Tank C was transferred to Tank A. In the end, there were 600 ml of water in each tank. What was the volume of water in Tank A at first?

Hi,

http://i47.tinypic.com/25jgr5s.jpg\">

One possible method: Work Backwards.

Can you make sense of the numbers?

Cheers



speedmaths.com


.

[Beikiasu]

tianzhu :thankyou:

[Beikiasu]

Hi, can someone help me to solve this problem sum?


1) Kumar had 50% more bookmarks than Leon. Max had 75% as many bookmarks as Kumar. Kumar and Leon gave Max a number of bookmarks in the ratio 3:1. As a result Max had twice as many bookmarks as before, and Leon had 16 bookmarks more than Kumar. How many bookmarks did Kumar give to Max? Ai Tong, 2011, Question 17, 5 mark, Ans:216.

2) There are two bags of jelly beans labelled A and B. In bag A, there are 470 red jelly beans and 480 green jelly beans. In bag B, there are 350 red jelly beans and 200 green jelly beans. Some red and green jelly beans from bag B are transferred to bag A. As a result, 60% of the jelly beans in Bag A and 20% of those in Bag B are red. How many red and how many green jelly beans are transferred from Bag B to Bag A?HP, 2011, Question 14, 4 mark, Ans: Red: 310, Green:40.

3) A contractor needed to cover an entire hall with tiles. On the first day, he laid 319 tiles. He completed tiling the rest of the hall in 7 days using an equal number of tiles each day. At the end of the 4th day, he was able to tile 8/15 of the hall. How many tiles did the contractor use to cover the entire hall? CHIJ, 2011, Question 15, 4 mark, Ans:1740 tiles.

Thanks

[Musicstar]

:thankyou:

speedmaths.com:

Musicstar:

Please help me to solve these questions. Thank you.

1) Tank A , B and C contained some water. 1/3 of the water in Tank A was transferred to Tank B. 1/4 of the water in Tank B was then transferred to Tank C . Lastly, 1/5 of the water in Tank C was transferred to Tank A. In the end, there were 600 ml of water in each tank. What was the volume of water in Tank A at first?

Hi,

http://i47.tinypic.com/25jgr5s.jpg\">

One possible method: Work Backwards.

Can you make sense of the numbers?

Cheers



speedmaths.com


.

[Musicstar]

http://i49.tinypic.com/1zouj5x.jpg\">


Hi,

I saw the working method but not really understand it. For this type of pattern question, is it must memorise the step of working. How to handle this type of question.

For question (a) is easy can do listing but for (b) if the number is very big not possible to do listing. What is the formula to do such question? Thank you.

[tianzhu]

Beikiasu:

2) There are two bags of jelly beans labelled A and B. In bag A, there are 470 red jelly beans and 480 green jelly beans. In bag B, there are 350 red jelly beans and 200 green jelly beans. Some red and green jelly beans from bag B are transferred to bag A. As a result, 60% of the jelly beans in Bag A and 20% of those in Bag B are red. How many red and how many green jelly beans are transferred from Bag B to Bag A?HP, 2011, Question 14, 4 mark, Ans: Red: 310, Green:40.

Hi

This question was discussed earlier in this thread.

Here was my response.

This question touches on SE.

You may use MD, UP or use letters of the alphabet to show the variables.

At first

Bag A

R:G ------ 470:480

Bag B

R:G ------ 350:200

After the transfer

Bag A

R:G ------ 3u:2u

Bag B

R:G ------ 1p:4p

3u + 1p ------- 820 (470 + 350)

2u + 4p ------ 680 (480 + 200)

12u + 4p ------ 3280

10u ------ 2600

1u ------ 260

Bag A

R:G ------ 3u:2u ------- 780:520

Red ----- 780 – 470 ------ 310

Green ----- 520 - 480 ------ 40

Best wishes

[tianzhu]

Musicstar:

For question (a) is easy can do listing but for (b) if the number is very big not possible to do listing. What is the formula to do such question? Thank you.

Hi

(n+1)*(n+2)/2 where n is the figure number

Best wishes

[Oldschool]

Beikiasu:

Hi, can someone help me to solve this problem sum?


1) Kumar had 50% more bookmarks than Leon. Max had 75% as many bookmarks as Kumar. Kumar and Leon gave Max a number of bookmarks in the ratio 3:1. As a result Max had twice as many bookmarks as before, and Leon had 16 bookmarks more than Kumar. How many bookmarks did Kumar give to Max? Ai Tong, 2011, Question 17, 5 mark, Ans:216.



Thanks

a)\tKumar had 50% more bookmarks than Leon

Ratio of Kumar to Leon
= 150 : 100
= 3 : 2
= 12 : 8 (Multiply by 4)

b)\tMax had 75% or ¾ as many bookmarks as Kumar

Ratio of Max to Kumar
= 75 : 100
= 3 : 4
= 9 : 12 (Multiply by 3)

c)\tSince there are 3 persons, so it is good to make the ratio in the form of K : L : M

K : L : M
= 12 : 8 : 9
= 48 : 32 : 36 ( Multiply by 4 to make computation easy later)

d)\tMax had twice as many as before after taking from Kumar and Leon

So, Kumar and Leon will give Max another 36.
But Kumar will give Max ¾ x 36 = 27, and
Leon will give Max ¼ x 36 = 9

e)\tBefore, K : L : M = 48 : 32 : 36

After, K : L : M = (48-27) : (32-9) : 72
= 21 : 23 : 72

Since after that, Leon had 16 more than Kumar, so
23U -21U = 16
U = 8

f)\tHow many did Kumar give Max?

27U = 27 x 8 = 216

Regards

[Oldschool]

Beikiasu:

Hi, can someone help me to solve this problem sum?


3) A contractor needed to cover an entire hall with tiles. On the first day, he laid 319 tiles. He completed tiling the rest of the hall in 7 days using an equal number of tiles each day. At the end of the 4th day, he was able to tile 8/15 of the hall. How many tiles did the contractor use to cover the entire hall? CHIJ, 2011, Question 15, 4 mark, Ans:1740 tiles.

Thanks

a)\t1st day + 7 days afterwards = total 8 days


1st day --- 319
2nd day --- U
3rd day --- U
4th day --- U
..
..
8th day -- U

Total tiles is (7U + 319)

For the first 4 days, 8/15 is completed.
Or 8/15 of the total tiles is used.

So last 4 days, 7/15 must be completed.
Or 7/15 of the total tiles must be used.

4U = 7/15 (7U + 319)

15 x 4U = 7 (7U + 319)

U = 203

Therefore, total = 7U + 319 = 7x203 + 319 = 1740

Regards