Q&A - PSLE Math

[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.

[Cheerfuldad]

Hi all,


Please help with the following questions. (Sorry do not know how to draw the pictures)

Q1. Two rectangular tanks A and B measures 40cm by 20cm by 40cm (height) and 50cm by 40cm by 45cm (height) respectively, Water is being filled by Tap P and Q at a rate of 1.2 litres/min and 5 litres/min in Tank A and Tank B respectively.
At 8 am, Tap P was turned on first.
a) What is the height of the water level in Tank A after 10 minutes?
b) At 8.10 am, Tap Q was then turned on. At what time will the height of the water level in both tanks equal?

Q2. There are 2 overlapping rectangles A and B. The area of rectangle B is 20% more than the area of rectangle A. The unshaded area of rectangle A is 80% of the unshaded area of rectangle B. What percentage of rectangle B is shaded?

Thank you.

[kavisuresh]

Pls help in solving these questions from 2009 top 10 school papers (prelim ) qns.

1. The average mass of some parcels in a box was 20kg at first. When another parcel which weighs 10kg is added to the box, the average mass becomes 18kg. How many parcels are in the box now ?

2. Alan completed a race in 1h 40min. In the race, he ran at an avg speed of 30m/min from pt A to pt B and then ran back from pt B to pt A at an avg speed of 20m/min. How long did he take to run back to pt A from pt B ?

3. At an enrichment camp, the number of boys was 45% of the number of girls. When 20% of the boys left the camp, there were 192 more girls than boys. How many children were at the camp at first ?

4. Given that p: (q+r)= 1:3, r: (q+s)=1:2, p:s = 2:5, a) find p:q:r:s b)find (r+q): (p+s)

5.Mdm Ang bought some highlighters, pens and mechanical pencils . 1/4 of them were highlighters. The number of pens she bought was 6 more than 1/2 the total number of all the items and the remaining were mechanical pencils. Each of the highlighters, pens and mechanical pencils cost @2.10, $4.05 and $1.60 respectively. She spent a total of $227.10 on all the items. How many items did she buy altogether ?

6.Mrs.Tan had 130 durians and mangosteens. After she sold 2/3 of the durians and 2/5 of the mangosteens , she had 36 more mangosteens than durians left. How many fruits had he left in all ?

7. Ahmad and Halim together took 5 days to paint the house. If Ahmad and Halim work together for 2 days, followed by Ahmad working alond for 8 days, Halim will take 1 more day to complete the remaining work.How long will Ahmad take to paint the house all by himself ?

8.Tracy counted the number of 10c coins, 20c coins and 50c coins in her piggy bank.The number of 10c coins was 24 more than the number of 50c coins. After spending 3/5 of the 10c coins, 1/4 of 20c coins and 18 50c coins,she had an equal number of 10c and 20c coins. The number of 50c coins now formed 40% of the remaining number of coins. a)How many 10c coins did Tracy have at first ?
b)How much did she spend in all ?

9. A bullet took 5hrs to travel from Patient town to Honest town while an electric train took 4hrs longer to travel from Honest town to Patient town. Both trains set off at the same time and moved towards each other. 2hrs later, they were 255km apart. what was the speed of the electric train ?

10. At carpark P, the number of lorries to that of vans was in the ratio 3:7. At carpark Q, the number of lorries to that of vans was in the ratio 8:9. When 40% more lorries from an industrial park entered carpark P and 20% of vans at carpark Q moved to carpark P, there were 76 fewer lorries at carpark P than at carpark Q. How many total vehicles were there altogether finally ?

Thanks a lot.