Q&A - PSLE Math

[peggy]

Tianzhu,


Much appreciated.

[Michaelia0816]

Hi Tianzhu! Thx and … I came straight to the point, can you help me with 3 question?


Here I go:
1)5 trained workers take 20 days to paint a room. 8 untrained workers can do the same task in 20 days. How long would a team of 4 trained workers and 4 untrained workers take to finish the same task?

2) 9 fewer students in the lower primany than the upper primany competed in the story telling this year. 2/3 of all those whol competed were boys. 3/7 of the lower primany participant were girls.1/4 of the participants in the upper primany were girls. How many boys took part in the competition

3) A box contained 50-cent coins, 20-cent coins and 10-cent coins in the ratio 3:2:1. 75% of the 50-cent coins were taken out and replaced by the same number of 10- cent coins. Then, 180 20-cent coins were taken out and replaced by the same number of 10-cent coins. In the end, the ratio of the number of 50- cent,20-cent and 10-cent coins became 3:4:17.
(a) What was the total number of coins taken out?
(b) Find the total value of coins taken out.

[tianzhu]

Hi


Hope this helps.

Best wishes

http://farm8.staticflickr.com/7246/7459644570_6087607dbd_z.jpg\">

[tianzhu]

peggy:

Tianzhu,


Much appreciated.

Hi

You're welcome.

Best wishes

[AJH]

tianzhu:

Hi


Hope this helps.

Best wishes

http://farm8.staticflickr.com/7246/7459644570_6087607dbd_z.jpg\">

:thankyou: very much.

[tianzhu]

AJH:

:thankyou: very much.

Hi

You're welcome.

Best wishes

[tianzhu]

Michaelia0816:

2) 9 fewer students in the lower primany than the upper primany competed in the story telling this year. 2/3 of all those whol competed were boys. 3/7 of the lower primany participant were girls.1/4 of the participants in the upper primany were girls. How many boys took part in the competition

Hi girl

Good Morning.

You may also work using “Units and Parts”, simply replace the bigger boxes with parts and smaller boxes with units.

Hope this helps.

Best wishes

http://farm9.staticflickr.com/8020/7463826400_2f86eb5e63_z.jpg\">

[tianzhu]

Michaelia0816:

Here I go:
1)5 trained workers take 20 days to paint a room. 8 untrained workers can do the same task in 20 days. How long would a team of 4 trained workers and 4 untrained workers take to finish the same task?

Hi

First thing first, where is your question from?

Please check with your teacher if it is within the syllabus.

There are a few approaches to solve this question which touches on inverse proportion.

I prefer not to work with fractions.

5 trained worker ------ 20 days
1 trained worker ------ 100 days

8 untrained worker ------ 20 days
1 untrained worker ------ 160 days

Consider 800 units as being used for painting of the room.

In 1 day, 1 trained worker ------- 800/100 ------ 8 units

In 1 day, 1 untrained worker ------- 800/160 ------ 5 units

In 1 day, 1 trained worker + 1 untrained worker ------ 13 units

In 1 day, 4 trained worker + 4 untrained worker ------ 52 units

Number of days -------- 800/52 ------- 15.38 days.(16 days)

Best wishes

[tianzhu]

Michaelia0816:

3) A box contained 50-cent coins, 20-cent coins and 10-cent coins in the ratio 3:2:1. 75% of the 50-cent coins were taken out and replaced by the same number of 10- cent coins. Then, 180 20-cent coins were taken out and replaced by the same number of 10-cent coins. In the end, the ratio of the number of 50- cent,20-cent and 10-cent coins became 3:4:17.
(a) What was the total number of coins taken out?
(b) Find the total value of coins taken out.

Hi

This question is crafted in such a way that it is neat to use MD. You may also work using units.

Due to time constraints, I’ll skip drawing the MD.

50 cents:20 cents:10 cents -------3:2:1 ------- 12:8:4

75% of the 50-cent coins were taken out and replaced by the same number of 10- cent coins.

Remove 9 units of 50 cents and add 9 units of 10 cents coins

Then, 180 20-cent coins were taken out and replaced by the same number of 10-cent coins.

Remove 180 20 cents coins and add 180 10 cents coins.

In the end

50 cents ------ 3 units (9 units taken out)
20 cents ------ 4 units (180 taken out)
10 cents ------- 17 units (9 units + 180)

4 units ------ 180
1 unit ------ 45

Number of coins taken out ------- (9*45) + 180 ------- 585

Value of 50 cents coins taken out ------- 405*50 ------ 202.50

Value of 20 cents coins taken out ------- 180*20 ------ 36

Total value of coins taken out -------- 238.50

Best wishes

[Michaelia0816]

I think this is not in the syballus but my teacher just gave us the Hw to be completed within 2 days, it hard, first time approaching such question, -.-