Q&A - PSLE Math

[2632parent]

Oh my goodness how silly of me, thank you I understand now. Well have another question on speed , please help.


1) Abdul, Bernard and Chi Hao were all standing in a straight line waiting for the race to start. Chi Hao was 300m ahead of Bernard and Bernard was 100m ahead of Abdul. At 9a.m, they started the race. Abdul overtook Bernard in 5mins.
In another 5 mins, Abdul overtook Chi Hao. If Bernard’s speed is 150m/mins, at what time did Bernard overtake Chi Hao?

Thank you very much

[jarenchuatw]

You right, Tianzhu. I forgot to put in the following info:


X:$8 per pair
Y: $6 perbpair
Z: $10 per pair

[jarenchuatw]

http://i50.tinypic.com/2ugyn3q.jpg\"> And for Q2, attaching the image here.

[tianzhu]

2632parent:

1) Abdul, Bernard and Chi Hao were all standing in a straight line waiting for the race to start. Chi Hao was 300m ahead of Bernard and Bernard was 100m ahead of Abdul. At 9a.m, they started the race. Abdul overtook Bernard in 5mins.
In another 5 mins, Abdul overtook Chi Hao. If Bernard's speed is 150m/mins, at what time did Bernard overtake Chi Hao?

Thank you very much

Hi

Good Morning.

For Speed questions, it helps to start with a simple diagram.

This question touches on motion in the same direction where the faster runner overtakes the slower one. An important point to note is at the point of overtaking, the distance covered by both runners will be the same.

Bernard was 100m ahead of Abdul with a speed of 150m/min
Abdul overtook Bernard in 5min.

In 5 min, Bernard covered 150*5 or 750m/min

Abdul ------- 100 + 750 ------ 850 m/min

Hence, Abdul’s speed ------- 850/5 ------ 170m/min

Chi Hao was 300m ahead of Bernard.This means Chi hao was 400 m ahead of Abdul.

In 10 min, Abdul covered 1700 m

In 10 min ,Chi Hao ran 1300 m

Chi Hao’s speed ------ 1300/10 ------- 130 m/min.

In 1 min, Bernard is 20 m faster than Chi Hao

In 15 min, Bernard is 300 m faster than Chi Hao.

Bernard overtook Chi Hao at 9.15 am

Best wishes

[2632parent]

Good morning tianzhu, thank you for the solution.

[tianzhu]

jarenchuatw:

You right, Tianzhu. I forgot to put in the following info:


X:$8 per pair
Y: $6 perbpair
Z: $10 per pair

Hi

First find the number of parts for the different brands of shoes at first.

Brand X ------ 3/7 ------ 12 parts

Brand Y ------ 4 parts (1/4 of 16 parts)

Brand Z ------- 12 parts.

Next, find the number of shoes sold per brand using “Number*Value”

Brand X ------ 1*8 ------ 8u

Brand Y ------ 2*6 ------ 12u

Brand Z -------4*10 ------- 40u

60u ------- 840

1u ------ 14

Number of shoes sold ------- 7*14 -------- 98

Total number of shoes@first ------ 98*5 ------- 490

Number of brand Z@first -------- 12/28*490 ------- 210

Best wishes

[tianzhu]

jarenchuatw:

http://i50.tinypic.com/2ugyn3q.jpg\"> And for Q2, attaching the image here.

Hi

Volume of water --------- 2000*60 ------- 120000

Tank A base area --------- 50*40 -------- 2000

Tank B base area --------- 70*40 -------- 2800

Height ( after pouring) -------- 120000/4800 ------- 25

Best wishes

[zombie]

Can someone teach me or help to solve these questions using the constant difference/unchanged total method ? Thanks a lot ! :oops:


1) \tThere were 165 more chickens than ducks on a farm. If 60% of the chickens and 20% of the ducks were sold, the number of chickens left will be twice the number of ducks left. How many chickens were sold?

2)\tThere were 40% of girls in the Science Club. After another 30 girls joined the
\tScience Club, the percentage of girls increased by 15%. How many pupils
\twere there in the club at the end ?

3)\tKelly had 40% as much money as Mandy. After Mandy spent $66 on a dress, the percentage of Kelly’s money increased to 60%. How much money did Kelly have?

4)\tAiling has 10% more money than Belle and Belie has 25% more money than Cally. If Ailing has $78 more than Cally, how much do the three of them hove?

5)\tAdam has 30% as many stickers than Ben and 25% more cards than Chris. If they have a total of 462 stickers, how many stickers does Chris have?

6)\tLucas drank 45% of a bottle of pepsi. If he drank another 1 35m1, he would have drank 75% of it. How much pepsi was there in the bottle at first?

7)\tMr Low had 40% more cows than sheep. After he sold 375 cows and bought
\t375 sheep, he had 80% lesser cows than sheep. How many sheep did he have in the end?

8)\tAnne, Ben and Chris shared the cost of their seafood dinner. Anne paid 40% the total amount and Ben paid 30% of what Anne and Chris paid. If Ben paid $36 less than Chris, how much did Anne pay?

[KoalaBear37]

I think for qn 6, the ans is 450ml.


Method:
75%-45%=30%
30%->135ml
100%->135/300 x 100
=450ml

To check:
Total amount of pepsi:450ml
45% of 450ml:202.5ml
75% of 450ml:337.5ml
Difference:30%
Difference in ml:135ml

Ans:450ml

[KoalaBear37]

I think for qn 6, the ans is 450ml.


Method:
75%-45%=30%
30%->135ml
100%->135/300 x 100
=450ml

To check:
Total amount of pepsi:450ml
45% of 450ml:202.5ml
75% of 450ml:337.5ml
Difference:30%
Difference in ml:135ml

Ans:450ml