Q&A - PSLE Math

[tianzhu]

mamona:

2. Tina, Suzy and Rachel have 144 stamps altogether. At first, Tina gave 12 stamps to Suzy. Then, Suzy gave 8 stamps to Rachel. After that, Rachel gave 20 stamps to Tina. The total number of stamps that Suzy and Rachel have now is half that of Tina has. The number of stamps that Suzy has now is 3/5 of the number of stamps that Rachel has. How many stamps did Tina and Rachel have altogether at first?

Hi

A student needs to see that the total number of stamps remains the same before and after.

In the end

Suzy ----- 3 units
Rachel ----- 5 units
Tina ------- 16 units

24 units ------ 144
1 unit ------- 6

Suzy ------- 18 stamps (in the end)

She received 12 stamps from Tina and gave 8 stamps to Rachel.

Hence, she had (18 – 12 + or 14 stamps at first

Therefore Tina and Rachel had (144 - 14) or 130 stamps at first.

Best wishes

[mamona]

Many Thanks for the Answer tianzhu. But atually the first question I worngly posted. I am looking for the solution for the below one.


1. Jug X and Jug Y contain different amounts of water at first. 50% of the water in Jug X was poured into Jug Y. Then 40% of the water in Jug Y was poured into Jug X. The final ratio of the amount of water in Jug X to the amount of water in Jug Y was 7 : 6.
a) What was the ratio of the amount of water in Jug X to the amount of water in Jug Y at first?
b) If there were 10 litres of water in Jug X at first, how much water was there in Jug X at the end?

Appreciate if you can give me the solution for this one.

[tianzhu]

mamona:

Many Thanks for the Answer tianzhu. But atually the first question I worngly posted. I am looking for the solution for the below one.


1. Jug X and Jug Y contain different amounts of water at first. 50% of the water in Jug X was poured into Jug Y. Then 40% of the water in Jug Y was poured into Jug X. The final ratio of the amount of water in Jug X to the amount of water in Jug Y was 7 : 6.
a) What was the ratio of the amount of water in Jug X to the amount of water in Jug Y at first?
b) If there were 10 litres of water in Jug X at first, how much water was there in Jug X at the end?

Appreciate if you can give me the solution for this one.

Hi

As similar to the earlier question, a simple pictorial representation may help students to see it better.

In the end

X : Y ------ 7:6 (after transfer of 40% to X)

Before X received 4 units from Y, it had 3 units (after transfer of 50% to Y)

Hence X had 6 units at first and Y had 7 units at first (10-3)

(a)X:Y ------ 6:7

(b)6 units ------ 10
7 units ------- 7/6*10 ------- 11 and 2/3 in the end

Best wishes

[small]

Hi,


am helping Tianzhu to do some amendment as there are some minor typo in the working.
[quote]
Hi

As similar to the earlier question, a simple pictorial representation may help students to see it better.

In the end

X : Y ------ 7:6 (after transfer of 40% to X)

Before X received 4 units from Y, it had 3 units (after transfer of 50% to Y)

Hence X had 6 units at first and Y had 7 units at first (10-3)

(a)X:Y ------ 6:7

(b)6 units ------ 10
7 units ------- 7/6*10 ------- 11 and 2/3 in the end

Best wishes[/quote]

[tianzhu]

small:

Hi,

am helping Tianzhu to do some amendment as there are some minor typo in the working.

Hi small

Thank You.

I'll do the corrections.

Best wishes

[Winx5015]

Hi,

Can someone help me with this question?

There were 4/5 as many sheep as horses in a zoo. After 92 horses were sent away, the percentage of horses dropped to 30%. Find the number of sheep in the zoo.

:thankyou:

[pixiedust]

Winx5015:

There were 4/5 as many sheep as horses in a zoo. After 92 horses were sent away, the percentage of horses dropped to 30%. Find the number of sheep in the zoo.

before :
sheeps -> 4U
horses -> 5U

after :
sheeps -> 7U
horses -> 3U

92 horses were sent away, no change in number of sheeps so make sheeps the same in before and after :

before :
sheeps -> 4U x 7 = 28U
houses -> 5u x 7 = 35U

after :
sheeps -> 7U x 4 = 28U
horses -> 3U x 4 = 12U

23U->92
U->4
Ans: There are 112 sheeps.

[anneshirleygilbert]

Hi. I need some help for the following questions:


1) Tom’s present age is thrice Sally’s age some years ago. Conversely, Sally’s present age is Tom’s age the same number of years ago. Given that the sum of their present ages is 30 years, how old is Tom now?

2)When Kok Hwa’s age was twice Bala’s age, Mike’s age was 30. When Mike’s age was twice Kok Hwa’s age, Bala’s age was 21. Given that Mike was the oldest among the three persons, find Bala’s age when Mike was 62 years old.

If possible, not by algebra, please.
Thank you in advance.

[tianzhu]

anneshirleygilbert:

Hi. I need some help for the following questions:

1) Tom's present age is thrice Sally's age some years ago. Conversely, Sally's present age is Tom's age the same number of years ago. Given that the sum of their present ages is 30 years, how old is Tom now?

Hi

Please follow this link.

http://www.kiasuparents.com/kiasu/forum/viewtopic.php?f=68&t=25129&start=430

http://farm8.staticflickr.com/7035/6812082325_7bb0b1b14f_z.jpg\">

Best wishes

[tianzhu]

anneshirleygilbert:

2)When Kok Hwa's age was twice Bala's age, Mike's age was 30. When Mike's age was twice Kok Hwa's age, Bala's age was 21. Given that Mike was the oldest among the three persons, find Bala's age when Mike was 62 years old.

Hi

For Q2,I'll provide some pointers instead of drawing MD.

Case 1
Bala ----- 1 unit
KH ----- 2 units
Mike ------ 30

Difference in age between KH and Bala ----- 1 unit

Difference in age between Mike and KH ----- 30 – 2 units

Case 2
Bala ----- 21
KH ----- 21 + 1 unit
Mike ------ (21 + 1 unit) + (21 + 1 unit)
Difference in age between Mike and KH ----- 21 + 1 unit

Difference in age between two people remains the same.

30 – 2 units ----- 21 + 1 unit

3 units ----- 9
1 unit ----- 3

When Mike’s age was 30, Bala was 3 years old.

62 – 30 ------ 32

Therefore , Bala ----- 3 + 32 ------ 35 years old.

Best wishes