Q&A - PSLE Math

[Dharma]

starlight1968sg:

Hello,

I need help on:
In a school, the ratio of the number of pupils wearing glasses to the number of pupils not wearing glasses is 11:5.
2/3 of the boys and 7/10 of the girls wear glasses.
What is the ratio of the number of boys to the number of girls?
Many thanks.

Wear glasses : No glasses = 11 : 5

(2u + 7p ) : (1u + 3p ) = 11: 5
10u + 35p = 11u + 33p
1u = 2p

No. of boys = 3u = 6p
No. of girls = 10p

Boys : Girls = 6 : 10 = 3 : 5

[starlight1968sg]

Dharma:

starlight1968sg:

Hello,

I need help on:
In a school, the ratio of the number of pupils wearing glasses to the number of pupils not wearing glasses is 11:5.
2/3 of the boys and 7/10 of the girls wear glasses.
What is the ratio of the number of boys to the number of girls?
Many thanks.

Wear glasses : No glasses = 11 : 5

(2u + 7p ) : (1u + 3p ) = 11: 5
10u + 35p = 11u + 33p
1u = 2p

No. of boys = 3u = 6p
No. of girls = 10p

Boys : Girls = 6 : 10 = 3 : 5

Thanks so much. I have been struggling with this prob, thinking I need to find the number of boys and girls...

[SLeng]

Hi Muffins,

In your answer for Mumbest’s question, what is LCM ?

Thanks

[starlight1968sg]

SLeng:

Hi Muffins,

In your answer for Mumbest's question, what is LCM ?

Thanks

LCM = lowest common multiple.

[starlight1968sg]

Dharma:

starlight1968sg:

Hello,

I need help on:
In a school, the ratio of the number of pupils wearing glasses to the number of pupils not wearing glasses is 11:5.
2/3 of the boys and 7/10 of the girls wear glasses.
What is the ratio of the number of boys to the number of girls?
Many thanks.

Wear glasses : No glasses = 11 : 5

(2u + 7p ) : (1u + 3p ) = 11: 5-------- (1)
10u + 35p = 11u + 33p-----------------(2)
1u = 2p

No. of boys = 3u = 6p
No. of girls = 10p

Boys : Girls = 6 : 10 = 3 : 5

Hi Dharma,
How to get from (1) to (2) ? I know you took (2u + 7p) * 5 and (1u+3p) *11 but why?
MTIA.

[pecalis]

starlight1968sg:

Dharma:

[quote=\"starlight1968sg\"]Hello,

I need help on:
In a school, the ratio of the number of pupils wearing glasses to the number of pupils not wearing glasses is 11:5.
2/3 of the boys and 7/10 of the girls wear glasses.
What is the ratio of the number of boys to the number of girls?
Many thanks.

Wear glasses : No glasses = 11 : 5

(2u + 7p ) : (1u + 3p ) = 11: 5-------- (1)
10u + 35p = 11u + 33p-----------------(2)
1u = 2p

No. of boys = 3u = 6p
No. of girls = 10p

Boys : Girls = 6 : 10 = 3 : 5

Hi Dharma,
How to get from (1) to (2) ? I know you took (2u + 7p) * 5 and (1u+3p) *11 but why?
MTIA.[/quote]See if I can help:

a:b = 2 : 1 means a is 2 times b.
Therefore, a = 2b

So if c : d = 5 : 11,
you cross multiply and get an equation of
11c = 5d

HTHs

[starlight1968sg]

pecalis:

See if I can help:


a:b = 2 : 1 means a is 2 times b.
Therefore, a = 2b

So if c : d = 5 : 11,
you cross multiply and get an equation of
11c = 5d

HTHs

Thanks a lot. Now it makes more sense to me.

[pecalis]

starlight1968sg:

pecalis:

See if I can help:


a:b = 2 : 1 means a is 2 times b.
Therefore, a = 2b

So if c : d = 5 : 11,
you cross multiply and get an equation of
11c = 5d

HTHs

Thanks a lot. Now it makes more sense to me.

You're welcomed.
My dd's psle is over but I still kapoy here sometimes.
I simply love to do Math! But honestly, my dd is faster than me!

[SLeng]

Thank you Starlight.

[Vanilla Cake]

tianzhu:

the kiasu student:

hi all,

My teacher gave us another question again.

At a fitness carnival,1600 people participated in a Mass Dance and Taiji. 30% of the Mass dance participants were adults. 40% of the Taiji participants were children. During a break, some Mass Dance participants went to join Taiji and some Taiji participants went to join the Mass Dance. After the change, 25% of the Mass Dance participants and 75% of the Taiji participants were adults. How many Mass Dance participants were there after the change?

Hi the kiasu student

Good Morning.

First, please take a few moments to compare your question with this one, (I think it’s from RGPS).

Container A contains 250 red marbles and 200 blue marbles.
Container B contains 600 red marbles and 150 blue marbles.
How many red and blue marbles must be moved from Container A to Container B such that 25% of the marbles in Container A are red and 75% of the marbles in Container B are red?

This RGPS question has two unknowns, and one can solve it with Simultaneously Equations(SE).If a student is comfortable with algebraic manipulation, he/she could use SE through substitution or elimination method.Otherwise, he/she may solve it with SE through visual representation using boxes or circles.

I think there is some missing information in your question. The concept is the total number of participants remains the same; you’ve the same number of adults and children in both scenarios.

Now compare your question with this one.

In Hall A, 30% of the 800 people were men. In Hall B, 40% of the 400 people were women and children. After some of the people in both halls had switched hall, 25% of the people in Hall A and 75% of those in Hall B were men.How many people are there in Hall B after the change?

Do you see the differences?There is a cap on the number of adults and the number of children,therefore, you'll get one answer.In your question, there are no limiting numbers, hence, I think you can have many answers.

I suggest you check with your teacher, please come back to share with other kids the solution once you get it.

May you be blessed with a successful PSLE 2010.

Best wishes

Hi Uncle Tianzhu/iFruit/atutor2001,

Could you pls visit this question first posted by \"the kiasu student\" on http://www.kiasuparents.com/kiasu/forum/viewtopic.php?p=270107.Below is the complete question which is from Singapore Chinese Girls' School (Primary) P6 Prelim 2010 Paper 2 Q17 [5 marks] set on 24 August 2010.

At a fitness carnival,1600 people participated in a Mass Dance and Taiji. 30% of the 1300 Mass Dance participants were adults. 40% of the Taiji participants were children. During the break, some Mass Dance participants went on to participate in Taiji, while some Taiji participants went on to participate in the Mass Dance. After the change, 25% of the Mass Dance participants and 75% of the Taiji participants were adults. How many Mass Dance participants were there after the change?
Answer given: 1260 participants

Pls kindly help to post the worked solution for my younger sister+other PSLE 2011 students to learn to solve this 5-mark question.
Thanks.