Q&A - PSLE Math

[peggy]

Hi Small,


Thanks for your solution.

Have a Great Day !!! :rahrah:

[mathfreak]

YumYum:

Dear Tianzhu,


Thank you.

I have another Qn:

The average mass of a group of girls is 38 kg. If one more pupil with a mass of 50 kg joins the group, the average mass will become 40 kg. Find the number of girls in the group first.

Thanks

Solution:
When the pupil with mass of 50 kg joins the group, imagine that the \"extra mass\" of the pupil, which is just 50 - 40 = 10 kg, is distributed among the other pupils of mass 38 kg. This means that the 10 kg is distributed among 10 ÷ (40 - 38) pupils, or 5 pupils. Hence, there were 5 girls in the group at first.
Just to be sure, we check: (38x5+50)÷6 is indeed 40.

[portal]

Thank you tianzhu and small for your solutions.

[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?

[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?