Q&A - PSLE Math

[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)

[small]

Hi,


HTH..
[quote] 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? [/quote]Since this is P6 question, we can use algebra method to solve:

Number of Boys = P
Number of girls = 40 – P

Number of trees planted by boys = 3P
Number of trees planted by girls = 2 x (40-P) -> 80-2P

Given that the boys planted 30 more trees than the girls;

(Number of trees planted by boys) – (Number of trees planted by girls) = 30
3P – (80-2P) = 30
3P - 80 + 2P = 30
5P = 110
1P = 22

There were 22 boys

[tianzhu]

match3frog:

- 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!

Hi

To make it more interesting, let’s imagine Mr and Mrs Li are hosting a party in a private room in a restaurant.

We have two scenarios here. The number of people in the room remains the same in these two scenarios.

1)When Mr Li shook hands with everyone else
2)When Mrs Li shook hands with everyone else.

If you refer to the MD, the number of women is shown by 1 unit + 1 (Mrs Li).

Besides MD, you may also use UM (Units Method) to solve this question.

So enjoy the moment and have fun.

Best wishes

http://farm8.staticflickr.com/7023/6644739703_59310c1a94_z.jpg\">

[jesschan]

Hi! Can someone please give me a copy of the answer sheet for Nanyang 2011 CA1 Maths Paper? I just ordered the exam papers and it will take another 5 days to receive them. My son has done the paper given by his friend and I hope I can mark it this weekend but too busy to do all the questions myself…

[match3frog]

Thank you kohkh, small & Tianzhu for taking time to answer the questions!

[Dazzle]

tianzhu:

match3frog:

- 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!

Hi

To make it more interesting, let’s imagine Mr and Mrs Li are hosting a party in a private room in a restaurant.

We have two scenarios here. The number of people in the room remains the same in these two scenarios.

1)When Mr Li shook hands with everyone else
2)When Mrs Li shook hands with everyone else.

If you refer to the MD, the number of women is shown by 1 unit + 1 (Mrs Li).

Besides MD, you may also use UM (Units Method) to solve this question.

So enjoy the moment and have fun.

Best wishes

http://farm8.staticflickr.com/7023/6644739703_59310c1a94_z.jpg\">

Hi Tianzhu,

I stumble upon this link and find it very useful. Being new, I am still trying to figure out the lingo used here. May I know what is MD? Also, will you show how to solve this using Unit Method? Thanks

[tianzhu]

Dazzle:

Hi Tianzhu,

I stumble upon this link and find it very useful. Being new, I am still trying to figure out the lingo used here. May I know what is MD? Also, will you show how to solve this using Unit Method? Thanks

Hi

MD refers to ‘Model Drawing” which is one of the many problem solving heuristics in primary maths.

In using UM, one basically uses ratios to work out the solution using a particular concept; in this case, the total number of people in the party remains the same.

Try it out first, if there is a need, I’ll post the solution at a later time.

Best wishes

[ksmama]

Hi, tianzhu, tks for reminder that can use units in equal total concept.

Soln in units method:
Case 1 mrs Li. M:W
3:1. (total 4 units)

Case2 mr Li. M:W
4:1. (total 5 units)

Since we knw total no of people shd b d same, convert the total units to the same using LCM of 4 n 5

So case 1 bcom. M:W
15:5 (prev no x 5)

Case 2. M:W
16:4 (previous no x 4)

Therefore no of men=16; women=5