Q&A - PSLE Math

[tianzhu]

portal:

I have this question to ask.Mrs Wong is 3 times as old as her son now.8 years ago,the ratio of Mrs Wong's age to her son's age was 7:1. What is Mrs Wong's age now?

Hi

You may use UM or MD.

The difference in age between two people stays the same.

Now
Mrs Wong: son ------- 3:1 ----- difference ------- (2)
Mrs Wong: son ------- 9:3 ------ difference ------- (6)

8 years ago
Mrs Wong: son ------- 7:1 ----- difference ------- (6)

Make the difference the same.

2 units ------ 8
1 unit ------ 4

Mrs Wong --------9*4 --------36

Best wishes

[small]

portal:

I have this question to ask.Mrs Wong is 3 times as old as her son now.8 years ago,the ratio of Mrs Wong's age to her son's age was 7:1. What is Mrs Wong's age now?

Hi,

HTH..

Current[
Mrs Wong : her son ------ 3u : 1u

8 years ago
Mrs Wong : her son ------ 3u-8 : 1u-8
Mrs Wong : her son ------ 7 : 1

Cross multiply
7(1u – = 3u-8
7u – 56 = 3u -8
4u = 48
1u = 12

Current Mrs Wong’s age ---- 3u = 3 x 12 = 36

Mrs Wong is 36 years old now

[small]

Hi portal,


Busy with son’s homework and did not realise that Tianzhu had provided the solution.

Tianzhu’s solution is much shorter and clearer.

[tianzhu]

bbkoala:

Hi Tianzhu


Thanks for your reply.
I managed to get the answer 30 using supposition, after reading your message.

Just can't understand the teacher's logic.
And DD insist it's the correct way (bcos teacher says so) but she can't explain why it's done this way.
This is what's worrying me

Hi

Questions of this genre are common in P5/P6 Maths.

You may want to have more questions to practise.

1) 20 boys and girls sold tickets for a funfair. Each ticket was sold at $5.Each boy sold 5 tickets and each girl sold 3 tickets. The amount collected by the boys was $20 more than the amount collected by the girls. Find a) how many girls were there in the group b) how many tickets were sold altogether? (8 boys, 12 girls, 76 tickets)

2) A class of 40 pupils helped to carry bundles of old newspapers in an event organised to collect funds for the old folks. Each boy carried 3 stacks of newspapers and each girl carried 2 stacks. Altogether, the boys carried 30 more stacks than the girls. What is the ratio of the number of boys to the number of girls in the class?

Best wishes.

[danishcookies]

Good day, I have 2 math Ques.

1) In a school choir, the ratio of the number of boys to the number of girls in is 2:3, 1/4 of the boys and 1/2 of the girls wear spectacles.If there are 48 pupils who wear spectacles. How many pupils are there in the choir?


2)John has $28 more than Peter. 1/3 of John’s money is equal to 4/5 of Peter’s money. Find John’s money.

[isetan]

hi tianzhu,


for question two, is the answer 11:9?

[tianzhu]

isetan:

hi tianzhu,


for question two, is the answer 11:9?

Hi

I am sorry. I don’t have the answer now.

I’ll give it to you later.

Best wishes

[portal]

tianzhu:

portal:

I have this question to ask.Mrs Wong is 3 times as old as her son now.8 years ago,the ratio of Mrs Wong's age to her son's age was 7:1. What is Mrs Wong's age now?

Hi

You may use UM or MD.

The difference in age between two people stays the same.

Now
Mrs Wong: son ------- 3:1 ----- difference ------- (2)
Mrs Wong: son ------- 9:3 ------ difference ------- (6)

8 years ago
Mrs Wong: son ------- 7:1 ----- difference ------- (6)

Make the difference the same.

2 units ------ 8
1 unit ------ 4

Mrs Wong --------9*4 --------36

Best wishes

Thank you Tianzhu and small

[portal]

small:

portal:

3)I have this question to ask as well.An empty retangular tank 0.5 meters long and 0.4 meters wide is filled with water from 2 taps,Tap A and Tap B.Tap A

was turned on and it fills the tank with water at a rate of 9 litres per minute.Tap B was turned on and it fills the tank with water at a rate of 11 litres per minute.What is the height of the water in the tank after Tap B was turned on for 10 minutes? leave your answer in meters. :imdrowning:

Hi,

Let me try to solve.

Base of the rectangular tank ----- 0.5m x 0.4m = 0.2 m square

I presumed Tap A and Tap B were turned on together
Every 1 minute ----- 11 + 9 = 20 litres
after 10 minutes ----- 20 x 10 = 200 litres = 0.2 m cube (1000 litres =1 m cube)

Height of tank x 0.2 m square =0.2 m cube
Height of tank = 1 m

In a exam will i get correct if i write 1m or 1.09m :?

[tianzhu]

danishcookies:

Good day, I have 2 math Ques.

1) In a school choir, the ratio of the number of boys to the number of girls in is 2:3, 1/4 of the boys and 1/2 of the girls wear spectacles.If there are 48 pupils who wear spectacles. How many pupils are there in the choir?

2)John has $28 more than Peter. 1/3 of John's money is equal to 4/5 of Peter's money. Find John's money.

Hi

Q1

Boys: Girls ------- 2:3 -------4:6

¼ of boys --------1u
½ of girls --------- 3u

1u+3u ----- 4u -------48
1u ------ 12
\t
10u ----- 12*10 ------ 120

Q2

1/3 of John's money ------ 4/5 of Peter's money.

Make the numerator the same.

4/12 of John's money ------ 4/5 of Peter's money.

John ------ 12 units
Peter ----- 5 units

7 units ------ 28
1 unit ----- 4

John ----- 12*4 ------48

Best wishes