Q&A - PSLE Math

[MathIzzzFun]

SaPan:

need help, please!


1.
there were 800 children in Group A and 30% of them were boys.
there were 400 children in Group B and 60% fo them were boys.
after some transfers between the two groups,
25% of children in Group A and 75% of children in Group B were boys.
How many children were transferred from Group B to A?

2.
Lilin collected 700 stickers and 35% of them were animal stickers.
Mina collected 300 stcikers and 55% of them were animal stickers.
After exchanging some stickers with each other,
20% of Lilin's stickers and 60% of Mina's stickers were animal stickers.
How many stickers did Mina get from Lilin?

Hi

hope this helps

Q1...

http://i55.tinypic.com/m9n69u.jpg\">

http://www.flickr.com/photos/62167097@N02/6160671185/in/photostream

Q2.. http://www.flickr.com/photos/62167097@N02/5897096477/in/photostream

cheers.

[tianzhu]

fxchow:

1) Mrs Gopal and Mrs Ari went to the supermarket.
Both women decided to spend all their money on either apples or pears and they would not buy the same fruit.
If Mrs Gopal bought only pears, she would have 9 more fruit than Mrs Ari.
If she bought only apples, she would have 41 more fruit than Mrs Ari.
How much more money has Mrs Gopal than Mrs Ari?
Ans: $12

Hi

This question has been discussed in one of the earlier posts.

Please refer to the solution from kancheongmum.

After reading Tianzhu post, lead me to solve this question using this method which is not new. The question of Tom spend $40 per day and Mary spend $80 per day and Mary would have $500 left when Tom has spent all his money .......

Apples : Pears ---- 40:60 ---- 2:3

1st case Ari spent 2/3 of Gopal 2nd case Ari spent 3/2 of Gopal
equal fraction 2/3 = 6/9 and 3/2 = 6/4

Gopal ()()()()()()()()() $5.40
Ari ()()()()()()

Gopal ()()()() $16.40
Ari ()()()()()()


9u + $5.40 = 4u + $16.40
5u ---- $11
1u ---- $2.20
Gopal money more than Ari by ---- 3u + $5.40 = (3 x $2.20) + $5.40
= $12

Best wishes

[SaPan]

MathIzzzFun:

...

Q1...
http://i55.tinypic.com/m9n69u.jpg\">

Q2.. http://www.flickr.com/photos/62167097@N02/5897096477/in/photostream

cheers.

thank you so much, MathIzzzFun!

pls allow me another question, :-
is it possible to solve such questions using units and parts?

[zsqchx]

Please help to solve the following question. Thanks.


Sam went shopping at a department store. He spent 1/5 of his money on a soft set and $800 on a washing machine. Later, he spent 1/8 of his remaining amount on dining table. If the amount of money left was $100 more than half of the amount he had at first, how much money did Sam have at first?

[Dharma]

zsqchx:

Please help to solve the following question. Thanks.


Sam went shopping at a department store. He spent 1/5 of his money on a soft set and $800 on a washing machine. Later, he spent 1/8 of his remaining amount on dining table. If the amount of money left was $100 more than half of the amount he had at first, how much money did Sam have at first?

If Sam had 100u at first
Spent 1/5 of sofa => 20u
Spent on washing machine => $800
Remainder => 100u – (20u +$800) = 80u - $800
Spent 1/8 of remainder on dining table; so he’ll be left with 7/8 of remainder i.e. (70u - $700)
(70u - $700) – (100u/2) = $100
20u - $700 = $100
20u = $800
1u = $40
Amt San had at first = 100u = $4000

[MathIzzzFun]

zsqchx:

Please help to solve the following question. Thanks.


Sam went shopping at a department store. He spent 1/5 of his money on a soft set and $800 on a washing machine. Later, he spent 1/8 of his remaining amount on dining table. If the amount of money left was $100 more than half of the amount he had at first, how much money did Sam have at first?

Hi

a model approach

http://www.flickr.com/photos/62167097@N02/5899971661/in/photostream

cheers.

[MathIzzzFun]

SaPan:

MathIzzzFun:

...

Q1...
http://i55.tinypic.com/m9n69u.jpg\">

Q2.. http://www.flickr.com/photos/62167097@N02/5897096477/in/photostream

cheers.

thank you so much, MathIzzzFun!

pls allow me another question, :-
is it possible to solve such questions using units and parts?

Hi SaPan,

yes, you can also solve such questions using the units and parts approach ie algebra... by the way, model approach is algebra in visual form.

cheers.

[fxchow]

MathIzzzFun:

fxchow:

Hi,


Can someone help to solve these two questions. TIA

1) Mrs Gopal and Mrs Ari went to the supermarket.
Both women decided to spend all their money on either apples or pears and they would not buy the same fruit.
If Mrs Gopal bought only pears, she would have 9 more fruit than Mrs Ari.
If she bought only apples, she would have 41 more fruit than Mrs Ari.
How much more money has Mrs Gopal than Mrs Ari?
Ans: $12

2) Talik was given some pocket money for recess. He realised that if he had spent $0.80 on each meal, he would have 8 meals fewer than if he had spent $0.60 per meal.
Talik spent $0.60 on 8 meals and spent $0.80 on the remaining meals. How many meals did the money last him?
Ans: $26

Hi fxchow,

Q1 is missing some information - costs of fruits for eg.

For Q2,

If Talik spent $0.60 per meal, he would have 8 more meals ---> 8 x 0.60 = $4.80. This amount was accumulated from spending $0.20 less per meal. So, number of $0.80 meals = $4.80 / 0.20 = 24

Amount of money he had = 24 x $0.80 = $19.20

After spending 8 x $0.60 meals, number of $0.80 meals he could have
= ($19.20 - $4.80) / $0.80
= 144 / 8
= 18

Total number of meals ($0.60 meals + $0.80 meals) = 8 x+ 18 = 26

cheers.

Hi MathIzzzFun,

Sorry, for question 1, each apple costs $0.40 while each pear costs $0.60.

Thanks!

[SaPan]

MathIzzzFun:

...

Hi SaPan,

yes, you can also solve such questions using the units and parts approach ie algebra... by the way, model approach is algebra in visual form.

cheers.

thanks again MathIzzzFun, I'll try and solve it using the unit and parts ways.

[Angel25]

A rectangular tank, 1m long, 80cm wide and 40cm high was filled with some water. 8 metal cubes of equal volume were placed in the water and 1200cm3 of water overflowed from the tank. Jacob then took 3 metal cubes from the water carefully and the height of the water in the tank was 37cm, (taking 1litre=1000cm3)

a) what was the volume of each metal cube?
b) what was the length of each metal cube?
c) how many litres of water were in the tank before 8 metal cubes were put in?