Q&A - PSLE Math

[Bunny27]

susutoo:

Can someone help to solve this problem:


80% of the children in the hall are girls. After 48 girls and 2 boys left the hall, the rest of the children are group into groups of 9 children. In each group there were 2 boys. Find the number of children in the hall at first.

Hi, someone pls help:
Abit confused..

A box contained some $1 coins and 50¢ coins in the ratio 2 : 3. Sean took out three $1 coins and exchanged for 50¢ coins. The money was then put back in the box and the ratio became 1 : 3. What is the sum of money in the box??

Thanks

[tianzhu]

susutoo:

Can someone help to solve this problem:


80% of the children in the hall are girls. After 48 girls and 2 boys left the hall, the rest of the children are group into groups of 9 children. In each group there were 2 boys. Find the number of children in the hall at first.

Hi

You may use \"Units and Parts\"

At first
Boys:Girls ----- 1unit (20%) :4 units (80%)

Change
Boys:Girls ----- -2: -48

In the end
Boys:Girls ----- 2 parts:7 parts

Equalise the parts or cross multiply.

1 unit - 2----- 2 parts
(x7)
7 units – 14 ------ 14 parts

4 units – 48 ------ 7 parts
(x2)
8 units – 96 ------ 14 parts

7 units – 14 ------ 8 units – 96
1 unit ------ 82

Number of children in the hall at first ------ 5*82 ------ 410

Best wishes

[susutoo]

Thanks!!

[tianzhu]

Bunny27:

A box contained some $1 coins and 50¢ coins in the ratio 2 : 3. Sean took out three $1 coins and exchanged for 50¢ coins. The money was then put back in the box and the ratio became 1 : 3. What is the sum of money in the box??
Thanks

Hi

You may use \"Units and Parts\"

three $1 coins ----- $3 ------ six 50¢ coins

At first
$1 coins: 50¢ coins ----- 2 units:3 units

Change
$1 coins: 50¢ coins ----- -3 : +6

In the end
$1 coins: 50¢ coins ----- 1 part :3 parts

Equalise the parts or cross multiply.

2 units – 3 ------ 1 part
(x3)
6 units – 9 ----- 3 parts

3 units + 6 ------ 3 parts

6 units – 9 ------ 3 units + 6

3 units ------ 15
1 unit ------ 5

10*1 ------ 10
15*0.5 ------ 7.5

Total ------ 17.50

Best wishes

[susutoo]

Two more Q:

1) the ratio of the sum, the different and the product f two whole number is 5:1:24. find the bigger number.

2) Tom bought some marker and files in the ratio 4:3. If the ratio of the total amount spent on markers to that of files was 2:1, find the ratio of the cost of marker to the cost of a file.

[MathIzzzFun]

susutoo:

Two more Q:

1) the ratio of the sum, the different and the product f two whole number is 5:1:24. find the bigger number.

2) Tom bought some marker and files in the ratio 4:3. If the ratio of the total amount spent on markers to that of files was 2:1, find the ratio of the cost of marker to the cost of a file.

Hi
Q1.

Larger number --> 3u
smaller number --> 2u
ratio of difference : product = 1 : 24 --> 6u = 24, u = 4
Larger number = 12, smaller number = 8

Q2.
cost per unit of markers : cost per unit of files = 2/4 : 1/3 = 1/2 : 1/3

cost of 1 marker : cost of 1 file = 3 : 2

cheers.

[superworried mum]

Hi, need help in this question,


I have some red and blue ribbons in a bottle.
If i add in 20 red ribbons, 60% of my ribbons are blue.
If i add in another 60 blue ribbons, 75% of mu ribbons are blue.
How many ribbons have I in the bottle?

Can there be two answers for this?
Thanks

[Synergy.042839Mom]

I have been using this forum to view Maths questions answered. I have some questions and will start posting them. Thanks to all the members for their support.

[tianzhu]

superworried mum:

Hi, need help in this question,


I have some red and blue ribbons in a bottle.
If i add in 20 red ribbons, 60% of my ribbons are blue.
If i add in another 60 blue ribbons, 75% of mu ribbons are blue.
How many ribbons have I in the bottle?

Can there be two answers for this?
Thanks

Hi

This question has been discussed in forums regularly.

Depending on one’s interpretation of the word another in the second condition, one may end up with 180 or 80.

It’ll be helpful if current PSLE students or their parents help to clarify with their school teachers on this question.

Best wishes

[Michaelia0816]

Someone help pls? A motorist took 3 h to travel from town A to town B. His average speed for the whole journey was 80 km/h. For the first 1/4 of the journey, he travelled at an average speed of 60km / h. Find his average speed for his remaining journey.