Q&A - PSLE Math

[3greatkids]

enoawng:

can anyone help?


John was n years old when his mother was 36 years old. Today, his mother is 3 times as old as John.
a) Express John’s age now in terms of n
b) What is John’s age now if n=8?

a) John's age now is (36-n)/2.
The theory is that the difference between mother's age and john's age never change, therefore, the difference in their age is always 36-n.
In order for the mother to be 3 times as old as John, when u draw the model, John will be 1 unit whereas mum is 3 units. their age difference(36-n) will then take up 2 units and john's age would be 1 unit. so in order to find 1 unit, you will take (36-n)/2

b) thus john's age now is (36-8)/2 which is 14

[James Ang]

Question asked:

Mary and Peter attended a party. Peter met with 4 times as many boy as girls while Mary met with 5 times as many boys as girls. How many boys and girls were at the party?

[3greatkids]

James Ang:

Question asked:

Mary and Peter attended a party. Peter met with 4 times as many boy as girls while Mary met with 5 times as many boys as girls. How many boys and girls were at the party?

not able to attach image....

anyway, let me try n explain:

first draw a model from peter's perspective. thus 1u= girls and 4u=boys.

When we put peter back in and mary out from the equation - cut a section out from girls and indicate 1. the cutout is used to represent mary. cut an equal part from each of the 4u and add 1 more to indicate peter.

The remainder from the cutout part from the girls is used to represent 1u from mary's perspective. after cutting the previous model, we have 4 equal units and 5 cutouts(including peter) thus we can deduce:

1u=5
5u=25(boys)

girls=1u + Mary = 5+1 = 6
[/img]

[tianzhu]

3greatkids:

not able to attach image....

Hi,you may insert image by following these links.

http://www.kiasuparents.com/kiasu/forum/viewtopic.php?t=2699&start=15
http://www.kiasuparents.com/kiasu/forum/viewtopic.php?t=3767&start=30

[3greatkids]

Hi tianzhu,


errmmmm I know how to insert img... juz that the \"add image to post\" was not working as it keeps showing webpage unavailable and I was lazy to do it the longer way . thanks anywayz! :celebrate:

[Dharma]

James Ang:

Question asked:

Mary and Peter attended a party. Peter met with 4 times as many boy as girls while Mary met with 5 times as many boys as girls. How many boys and girls were at the party?

http://www.postimage.org/

[Dharma]

David Koriadi:

Sandy bought some apples and oranges. The number of apples was 1 ¼ times the number of oranges. After she packed the apples into boxes of 10 and oranges into boxes of 6, she found that she had 2 more boxes of oranges than apples. How many apples did she buy at first?

http://www.postimage.org/

[Tang]

Dharma:

James Ang:

Question asked:

Mary and Peter attended a party. Peter met with 4 times as many boy as girls while Mary met with 5 times as many boys as girls. How many boys and girls were at the party?

http://www.postimage.org/

If we substitute p = 5 into the model for Mary,
Boys + Peter = 5 x 5 + 1 = 26 boys [should be 25]

Girls + Mary = 5 - 1 + 1 = 5 girls [should be 6]


There is an error in labelling in the model for Mary. Should be

Mary met --> Boys (p - 1) ; Girls (p) ; Peter (1)

you will then get 25 boys and 6 girls.

[Dharma]

Thanks Tang.

http://www.postimage.org/

[N3SKiasu]

Hi, kindly help with this question:


In a classroom, when a boy stands up, the number of boys sitting becomes 4/5 of the number of girls sitting. On the other hand, when a girl stands up, the number of girls sitting becomes 8/7 of the number of boys sitting. How many boys and girls are there in the class altogether?

Question looks similar to the Mary & Peter question but still can't figure out. :oops: pls help.