Q&A - PSLE Math

[smileplease]

Need help :


Chan cycled from the post office to the library at a constant speed. At the same time, Valerie cycled from the library to the post office at a constant speed. 20 minutes later, they passed each other. Chan took another 16 minutes to reach the library, while Valerie was still 1.53km away from the post office.
a) what was the speed of Valerie? Give your answer in m/min
b) what was the distance between the post office and the library?

[MathIzzzFun]

smileplease:

Need help :


Chan cycled from the post office to the library at a constant speed. At the same time, Valerie cycled from the library to the post office at a constant speed. 20 minutes later, they passed each other. Chan took another 16 minutes to reach the library, while Valerie was still 1.53km away from the post office.
a) what was the speed of Valerie? Give your answer in m/min
b) what was the distance between the post office and the library?

Hi

there are a couple of ways to solve this.... here's one using combined speed.

Chan & Valerie took 20 min to cycle the total distance from library to post office (when they passed each other).

after they passed each other, they cycle another 16 min and Valerie was still 1.53km away from post office..
so, 4 min = 1.53km
20 min = 5 x 1.53 km = 7.65 km so the distance between post office and the library is 7.65km.

Distance cycled in 36 min by Valerie = 7.65 km - 1.53km = 6.12km
Valerie's speed = 6120m/36 = 170 m/min

cheers.

[Alchemist]

Hi - need some help for this sum from SHHK maths prelim 2011 paper 2.


There were a total of 930 boys and girls at a carnival. After 4/5 of the boys and 3/4 of the girls left, there were 120 more girls than boys that remained. How many boys were at the carnival at first?

Thanks in advance.

[PiggyLalala]

vidhyalog:

Hi - need some help for this sum from SHHK maths prelim 2011 paper 2.


There were a total of 930 boys and girls at a carnival. After 4/5 of the boys and 3/4 of the girls left, there were 120 more girls than boys that remained. How many boys were at the carnival at first?

Thanks in advance.

This is what my ds will do for such question.
Let the number of boys be 5p and the number of girls be 4u.
therefore 5p + 4u = 930.-----(1)
4/5 boys left, that is, 1/5 boys stayed. Therefore p boys remained.
3/4 girls left, that is, 1/4 girls stayed. Therefore u girls remained.
There are 120 more girls than boys, that is, u = p + 120.------(1)
hence from (1) and (2): 5p + 4(p+120) = 930
5p + 4p + 480 = 930
9p = 450
p = 50.

Boy: 5p = 250.

this is a simplified simultaneous equation but I think most pupils can understand

[Alchemist]

PiggyLalala:

vidhyalog:

Hi - need some help for this sum from SHHK maths prelim 2011 paper 2.


There were a total of 930 boys and girls at a carnival. After 4/5 of the boys and 3/4 of the girls left, there were 120 more girls than boys that remained. How many boys were at the carnival at first?

Thanks in advance.

This is what my ds will do for such question.
Let the number of boys be 5p and the number of girls be 4u.
therefore 5p + 4u = 930.-----(1)
4/5 boys left, that is, 1/5 boys stayed. Therefore p boys remained.
3/4 girls left, that is, 1/4 girls stayed. Therefore u girls remained.
There are 120 more girls than boys, that is, u = p + 120.------(1)
hence from (1) and (2): 5p + 4(p+120) = 930
5p + 4p + 480 = 930
9p = 450
p = 50.

Boy: 5p = 250.

this is a simplified simultaneous equation but I think most pupils can understand

Thank you. It was something my son understood.

[Daddy]

Hi Tianzhu,


sorry for asking again.

I’m still not understand how you got 2/8 (2 units) from 25% of quail eggs.
left.
Why not 3 units or more. Thanks.

[Cheerfuldad]

Hi all,


Need your help!

Q1. Michelle had 60% more cards than Adila. Usha had 35% fewer cards than Michelle. Michelle and Adila gave Usha some cards in the ratio of 3:1. As a result, Usha had 1 1/2 times as many cards as before. Given that Michelle had 238 more cards than Adila in the end, how many cards did Michelle give to Usha?

TIA

[tianzhu]

Daddy:

Hi Tianzhu,


sorry for asking again.

I'm still not understand how you got 2/8 (2 units) from 25% of quail eggs.
left.
Why not 3 units or more. Thanks.

Hi

No worries.

Please refer to the MD.

After he sold 6 units of quail eggs, he found that he had 25% of his quail eggs.

Number of quail eggs sold ------ 6 units
Number of quail eggs left ------ 2 units
Total number of quail egg ------- 8 units.

You need to add 2 units to 6 units to make 8 units because 2/8 gives 1/4 which is also 25%.

Best wishes

http://farm7.static.flickr.com/6192/6146804950_c011b6a6d6_z.jpg\">

[Hifive]

Hi


Need help with this question:

A group of pupils calculated their average score for a Science Test. They noted that:

if anyone of them scored 13 marks more, their average score would be 90
if anyone of them scored 5 marks less, their average score would be 87

How many pupils were there in the group?

[tianzhu]

Hifive:

A group of pupils calculated their average score for a Science Test. They noted that:

if anyone of them scored 13 marks more, their average score would be 90
if anyone of them scored 5 marks less, their average score would be 87

How many pupils were there in the group?

Hi

13 marks more and 5 marks less, this means a gap of 18 marks.

The difference in average mark is 3 (90-87)

18/3 ----- 6
18 marks are distributed among 6 students.

The answer is 6.

Best wishes.