Q&A - PSLE Math

[Dharma]

iFruit:

oovi-yah:

pls help me on these 3 questions


3.Mrs.raju bought 20 bottles of milk and 5 boxes of cornflakes from supermarket.if she had bought these items at 20% discount,the amount of money she saved could buy another 3 more boxes of cornflakes at the usual price.the usual price of a bottle of milk was 2.15.what was the usual price of a box of cornflakes?

20% of 20 bottles of milk = 1/5 x 20 x2.15 = 8.6

Let price of a box of cornflakes = u

20% of 5 boxes of cornflakes = 1/5 x 5 x u = u

8.6 +u = 3u ----> 2u = 8.6 ---> u = 4.3

Usual price of a box of cornflakes = $4.30

4 bottles of Milk + 1 box of cornflakes = 3 boxes of cornflakes
2 boxes of cornflakes = 4 bottles of milk
1 box of cornflakes = 2 bottles of milk = 2 x $2.15 = $4.30

[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.

[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!