Q&A - PSLE Math

[Neat]

just888:

Neat:

1) The ratio of the number of Donovan's stickers to the number of Hong Yi's stickers is 10:3. After Donovan gave Hong Yi 1/5 of his stickers, Hong Yi had 30 stickers less than Donovan. How many stickers did Donovan give to Hong Yi?

1/5 of 10 units is 2 .
After giving Donovan's stickers : HongYi's stickers is 8:5
Difference in units is 3.
3 units = 20 stickers
1 units 10.
Donovan gives Hong Yi 2 unit therefore, 2x10 = 20 stickers.

Neat:

2) Class A and Class B have the same number of pupils. The ratio of the number of boys in Class A to the number of boys in Class B is 3:2. The ratio of the number of girls in Class A to the number of girls in Class B is 3:5. Find the ratio of the number of boys in Class A to the number of girls in Class B.

Class A boys to Class B boys is 3:2
Class A girls to Class B girls is 3:5

Common multiple of 2, 3, 5 is 30. Therefore:

Class A boys to Class B boys is : 10:15
Class A girls to Class B girls is : 10: 6

Hence, Class A boys to Class B girls is 10:6

Hi just888

Thanks for help.

The answer for Q2 is 6:5.

[tianzhu]

Neat:

:rahrah: :rahrah: :rahrah:
Hi Tianzhu,
Thank you so much!!!

Hi Neat

Good Morning.

You're welcome.

Hope this helps.

Best wishes.

http://farm8.staticflickr.com/7142/6623800383_1c4c031586_z.jpg\">

[just888]

tianzhu:

Neat:

:rahrah: :rahrah: :rahrah:
Hi Tianzhu,
Thank you so much!!!

Hi Neat

Good Morning.

You're welcome.

Hope this helps.

Best wishes.

http://farm8.staticflickr.com/7142/6623800383_1c4c031586_z.jpg\">

Tianzhu,
Thanks for the clear explaination. Guess I need to re-study my math too.

[match3frog]

Hi,


Please help with the following questions:

1) Box A contains 50 cent coins and Box B contains 20 cent coins. There are 19 more coins in Box B than in Box A. But the amount of money in Box A is $1.30 more than in Box B. How much money is in Box A?

2) On Tree-planting day, 40 pupils planted some trees. Each boy planted 3 trees and each girl planted 2 trees. The boys planted 30 more trees than the girls. How many boys were there?

- My dd always have problems with this type of questions. How to teach her to solve them?

3) A group of people met at a party. Each person shook hands with everyone else. Mr Li shook hands with 3 times as many men as women. Mrs Li shook hands with 4 times as many men as women. How many men and how many women were there at the party.

Thanks!

[mrswongtuition]

For question 1:

19 x 20 cents = $3.80
$1.30+$3.80 = $5.10
$5.10 divide ($0.50-0.20) = 17
There are 17 50-cent coins.

[match3frog]

mrswongtuition:

For question 1:

19 x 20 cents = $3.80
$1.30+$3.80 = $5.10
$5.10 divide ($0.50-0.20) = 17
There are 17 50-cent coins.

Hi Mrs Wong,

Thanks for your solution. Can you pl explain it?

[mrswongtuition]

For Q2, try trial & error.

Draw 6 columns.
Column 1: Number of boys
Column 2: Boys x 3
Column 3: number of girls
Column 4: girls x 2
Column 5: Column 2 - Column 4
Column 6: Check

Answer is 22 boys & 18 girls.

[mrswongtuition]

match3frog:

mrswongtuition:

For question 1:

19 x 20 cents = $3.80
$1.30+$3.80 = $5.10
$5.10 divide ($0.50-0.20) = 17
There are 17 50-cent coins.

Hi Mrs Wong,

Thanks for your solution. Can you pl explain it?

Sorry, typed that on my iPhone and it's tedious to type long explanations.

There are 19 more 20-cent coins than 50-cents coins.
The value of these coins is:
19 x 20 cents = $3.80

Adding the excess and the 'extra amount':
$1.30+$3.80 = $5.10
(This will be how much more money there will be from 50-cent coins compared with 20-cents coins if there is equal number of 50-cent and 20-cent coins.)

Divide $5.10 by the difference in value of each 50-cent coin and each 20-cent coin:
$5.10 divide ($0.50-0.20) = 17

There are 17 50-cent coins

[match3frog]

Mrs Wong,


Thanks so much for your solutions and explanation!

[kohkh]

match3frog:

Hi,


Please help with the following questions:

1) Box A contains 50 cent coins and Box B contains 20 cent coins. There are 19 more coins in Box B than in Box A. But the amount of money in Box A is $1.30 more than in Box B. How much money is in Box A?

2) On Tree-planting day, 40 pupils planted some trees. Each boy planted 3 trees and each girl planted 2 trees. The boys planted 30 more trees than the girls. How many boys were there?

- My dd always have problems with this type of questions. How to teach her to solve them?

3) A group of people met at a party. Each person shook hands with everyone else. Mr Li shook hands with 3 times as many men as women. Mrs Li shook hands with 4 times as many men as women. How many men and how many women were there at the party.

Thanks!

Mr Li shook hands with 15 men and 5 women
Mrs Lee shook hands with 16 men and 4 women

Total Men = 16 (including Mr Li himself)
Total Women = 5 (including Mrs Li herself)