Q&A - PSLE Math

[mathfreak]

Superbugs:

Nan Hua CA1 P6 2011

Q15
A farm has some ducks and cows.
The ratio of the number of animals to the total number of legs is 8:23.
Express the number of ducks as a fraction of the cows.
Give your answer in the simplest form.
Pls assist with this question. Tks

Solution:
Pairing a cow and a duck, the two animals have 6 legs.
Hence in a situation where there are equal numbers of cows and ducks, the ratio is 2 : 6 = 8 : 24.
However, the ratio is now 8 : 23.
The difference in legs is 24-23=1 unit. Since the difference in number of legs between a cow and a duck is 2, we let 1 unit be 2 legs. By this assumption, the total number of animals is 16.
If we decrease 1 cow and increase 1 duck, the number of legs decreases by 2.
Hence, there are 7 cows and 9 ducks.
Ans: 9/7 = 1 2/7

[mathfreak]

peggy:

Please help !


The ratio of the amount of money in jane's account to the amount of money in May's account was 11:7. Jane and May shared the cost of a computer in the ratio of 3:1. Jane used 1/2 of her money to pay for her share of the computer. May had $620 left after paying for her share. What was the cost of the computer?

Thanks!

Solution:
We increase the ratio such that it is 22:14 (this is for easier calculation).
1/2 of Jane's money is 11 units.
The amount May paid is therefore 11/3 units.
14 - 11/3 = 10 1/3 units.
Hence $620 is 10 1/3 units.
11 + 11/3 = 14 2/3 units.
14 2/3 units is $880.
Ans: $880

[mathfreak]

Superbugs:

Nan Hua CA1 P6 2011

Q14.
My salary is 1/5 more than my sister but 20% less than my brother. If our total salary is $11,100, what is my sister's salary?

If Me=100%
Brother =120%
Sister=80%
80/300x11,100=2960
but answer is $3000?
Pls assist. Tks

Actually, if Me is 100%, Sister is not 80% (this means \"Me\" had 1/4 more than Sister), but instead is 100%*5/6=83 1/3%. This is so that 1/5 of Sister added to Sister will give \"Me\".
Brother is also not 120% (this means \"Me\" had 16 2/3% less than Brother), but instead is 100%*5/4=125%. This is so that 20% of Brother subtracted from Brother will give \"Me\".
The total would be 308 1/3%, which means 83 1/3% is $3000.

[small]

Superbugs:

Nan Hua CA1 P6 2011

Q14.
My salary is 1/5 more than my sister but 20% less than my brother. If our total salary is $11,100, what is my sister's salary?

If Me=100%
Brother =120%
Sister=80%
80/300x11,100=2960
but answer is $3000?
Pls assist. Tks

Hi,

HTH..

My salary is 1/5 more than my sister but 20% less than my brother. If our total salary is $11,100, what is my sister's salary?

Sister : Me : Brother
100 : 120 : 150 (120/0.8)
10u : 12u : 15u

37u = 11100
1u = 300

My sister ----- 10u ------ 10 x 300 = 3000

[danishcookies]

1) In a school choir, the ratio of the number of boys to the number of girls in is 2:3. 1/4 of the boys and 1/2 of the girls wear spectacles. If there are 48 pupils who wear spectacles, how many pupils are there in the choir?


2) John has $28 more than Peter. 1/3 of John’s money is equal to 4/5 of Peter money. Find John money?

[Superbugs]

small:

Superbugs:

Nan Hua CA1 P6 2011

Q14.
My salary is 1/5 more than my sister but 20% less than my brother. If our total salary is $11,100, what is my sister's salary?

If Me=100%
Brother =120%
Sister=80%
80/300x11,100=2960
but answer is $3000?
Pls assist. Tks

Hi,

HTH..

My salary is 1/5 more than my sister but 20% less than my brother. If our total salary is $11,100, what is my sister's salary?

Sister : Me : Brother
100 : 120 : 150 (120/0.8)
10u : 12u : 15u

37u = 11100
1u = 300

My sister ----- 10u ------ 10 x 300 = 3000

Tks a lot! Got to use sister as 100%.

[Superbugs]

mathfreak:

Superbugs:

Nan Hua CA1 P6 2011

Q14.
My salary is 1/5 more than my sister but 20% less than my brother. If our total salary is $11,100, what is my sister's salary?

If Me=100%
Brother =120%
Sister=80%
80/300x11,100=2960
but answer is $3000?
Pls assist. Tks

Actually, if Me is 100%, Sister is not 80% (this means \"Me\" had 1/4 more than Sister), but instead is 100%*5/6=83 1/3%. This is so that 1/5 of Sister added to Sister will give \"Me\".
Brother is also not 120% (this means \"Me\" had 16 2/3% less than Brother), but instead is 100%*5/4=125%. This is so that 20% of Brother subtracted from Brother will give \"Me\".
The total would be 308 1/3%, which means 83 1/3% is $3000.

Tks a lot! I realised my mistake.

[small]

Superbugs:

Tks a lot! Got to use sister as 100%.

You are welcome...

[MathIzzzFun]

danishcookies:

1) In a school choir, the ratio of the number of boys to the number of girls in is 2:3. 1/4 of the boys and 1/2 of the girls wear spectacles. If there are 48 pupils who wear spectacles, how many pupils are there in the choir?


2) John has $28 more than Peter. 1/3 of John's money is equal to 4/5 of Peter money. Find John money?

Hi
1)
Boys -->12 units, Girls --> 18 units, total 30 units
Boys with specs --> 3 units
Girls with specs --> 9 units
12 units --> 48, 1 unit --> 4

Total number of pupils in choir --> 30 x 4 = 120

2)
4/5 Peter's money = 1/3 John's money = 4/12 John's money
John's money --> 12 units
Peter's money --> 5 units
7 units --> $ 28, 1 unit --> $4
John's money --> 12 x $ 4 = $ 48

cheers.

[peggy]

Hi Small,


I understand that my salary is 20% less than my brother, but you get 120/0.8?