Q&A - PSLE Math

[Superbugs]

Man Hua CA1 P6 2011

Q11.
Rectangle A overlaps with Rectangle B. Rectangle A is twice the size of Rectangle B. If 1/3 of Rectangle B overlaps with Rectangle A, what fraction of Rectangle A overlaps with Rectangle B?

[Superbugs]

Superbugs:

Man Hua CA1 P6 2011

Q11.
Rectangle A overlaps with Rectangle B. Rectangle A is twice the size of Rectangle B. If 1/3 of Rectangle B overlaps with Rectangle A, what fraction of Rectangle A overlaps with Rectangle B?

Actually this is very easy. I got the answer as 1/6. Tks

[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

[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!

[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

[mathfreak]

Superbugs:

Nan Hua CA1 P6 2011

Q7:
I have some red and blue ribbons in a bottle.
If I add in 20 red ribbons, 60% of my ribbons are blue.
If I add in another 60 blur ribbons, 75% of my ribbons are blue.
How many ribbons have I in the bottle?
Please help with this question. Tks

Not sure about using model method for this one but here is how I solved this type of question when I was in primary school:
Let x be the number of red ribbons and y be the number of blue ribbons.
Then: (x+20)/y = 40/60 = 2/3
and x/(y+60) = 25/75 = 1/3
Solving the simultaneous equations for x and y we get:
2y = 3x + 60, and 3x = y + 60
Hence y = 60 + 60 = 120.
x = 60.
x+y = 120 + 60 = 180.
Ans: 180 ribbons.

[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