Q&A - PSLE Math

[underthesea]

Thanks Guan Hui and Maths Monster for your reply.


Here’s another problem I can’t solve. Need your help.

A class has 44 pupils. 3/4 of the boys and 2/5 of the girls are short-sighted. There are 26 boys and girls short-sighted. How many more boys than girls in the class.

[Vanilla Cake]

underthesea:

A class has 44 pupils. 3/4 of the boys and 2/5 of the girls are short-sighted. There are 26 boys and girls short-sighted. How many more boys than girls in the class.

Hi underthesea,

I am the younger sister of Vanilla Cake and your question is similar to this question posted in another forum.

Hogwarts photography club has 1150 members.20% of the men and 25% of the women are non-professional photographers. A total of 250 members are non-professional photographers. How many more men than women are there in the club?

There are 2 different solutions given and let's wait for Guan Hui and Maths Monster to come up with preferably model solutions.

Solution 1
3/4 Boys + 2/5 Girls = 26 (Short-sighted)
Multiply by 5/2,
15/8 Boys + Girls = 65

Boys + Girls = 44

7/8 Boys =21
Boys = 24
Girls = 44-24=20

Difference = 24-20 = 4
There are 4 more boys than girls in the class.

Solution 2
Boys
S : N
3 : 1

Girls
S : N
2 : 3

S: Short-sighted
N: Normal vision

Since units for boys are not the same as units for girls, let's use u for Boys' units and p for Girls' units.

3u+2p = 26 (short-sighted)
1u+3p = 18 (normal vision) - *
* - (Multiply by 3)
3u+9p = 54

9p-2p = 54-26
7p = 28
p = 4

Girls: 5p = 5x4 = 20
Boys: 44-20 = 24

Difference = 24-20 = 4
There are 4 more boys than girls in the class.

Thank you.

[Maths Monster]

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[underthesea]

Hi,


Thanks for your reply. If, say the child doesn't know how to do this question is exam. Given that the total number of pupils is not big, can the child use Guess and Check method to solve this problem?

We know the number of boys and girls must be a whole number and the number of boys is a factor of 4 while the number of girls is a factor of 5.

So, for boys => 4, 8, 12, 16, 20, 24, 28, 32, 36, 40
for girls = > 5, 10, 15, 20, 25, 30, 35, 40

From the above, we can figure out 24 + 20 = 44. Hence, there are 4 more boys than girls.

Do you think marks will be awarded? :?

[skyjuice]

Does anyone have any comment or feedback on Fabian Ng’s Math classes? I’m considering sending my son as he’s rather weak and it’s PSLE yr for him. A friend said he’s good for her son but each 1.5hr class is $75. With such fees, I would like to know more of his classes if anyone cares to share. Thanks!!

[Maths Monster]

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[Emelyn]

Hi,


I have a question :

In a soccer stadium, the number of female to male spectators is 3:7. After 287 female and 287 male left the stadium, the ratio of female to male spectators became 2:5. How many spectators were there at first ?

Can someone help me solve ?

[James Ang]

an interesting thinking question to share here.


Mainah had some money at first.she spent it all in 3 stores.In each store, she spent $2 more than half of what she had when she entered.
(a) How much did she spend at the last store?
(b)how much did she have at first?

[Dharma]

Emelyn:

Hi,


I have a question :

In a soccer stadium, the number of female to male spectators is 3:7. After 287 female and 287 male left the stadium, the ratio of female to male spectators became 2:5. How many spectators were there at first ?

Can someone help me solve ?

Female : 3u – 287 = 2p
Male : 7u – 287 = 5p

15u – 1435 = 10p
14u – 574 = 10p

15u – 1435 = 14u – 574
1u = 861

No. of spectators in the stadium at first = 10u = 861 x 10 = 8610

[ChiefKiasu]

James Ang:

an interesting thinking question to share here.


Mainah had some money at first.she spent it all in 3 stores.In each store, she spent $2 more than half of what she had when she entered.
(a) How much did she spend at the last store?
(b)how much did she have at first?

(a) Amount spent in last store = S = S/2 + 2
=> Half of S = $2
=> S = $4

(b) Money Mainah had when entering 2nd store = $4 + $4 + $2 = $10
Money Mainah had when entering 1st store = $10 + $10 + $2 = $22

So Mainah had $22 at first.