Q&A - PSLE Math

[peggy]

Thanks, Tianzhu!

[Winx5015]

Thanks charsen and tianzhu.


Good nite

[MathIzzzFun]

zombie:

Can someone teach me or help to solve these questions using the constant difference/unchanged total method ? Thanks a lot ! :oops:


1) \tThere were 165 more chickens than ducks on a farm. If 60% of the chickens and 20% of the ducks were sold, the number of chickens left will be twice the number of ducks left. How many chickens were sold?

Left --> 40% (=2/5) of chickens and 80% (=4/5) of ducks

Chickens left : Ducks left = 2 : 1 --> 8 units : 4 units

Number of chickens at first --> 8 units ÷ 2/5 = 20 units
Number of ducks at first --> 4 units ÷4/5 = 5 units

There were 165 more chickens than ducks, so
20 units - 5 units = 15 units --> 165
1 unit --> 11

Number of chickens sold --> 3/5 x 20 x 11 = 132

cheers,

[MathIzzzFun]

zombie:

Can someone teach me or help to solve these questions using the constant difference/unchanged total method ? Thanks a lot ! :oops:


2)\tThere were 40% of girls in the Science Club. After another 30 girls joined the Science Club, the percentage of girls increased by 15%. How many pupils were there in the club at the end ?

At first,
total number of pupils in Science club --> 100 units
number of girls in Science club --> 40 units

15% x 40 units = 6 units --- total 106 units
6 units --> 30
1 unit --> 5

Total number of pupils in Science club, after 30 girls joined --> 106 x 5 = 530

cheers.

[MathIzzzFun]

zombie:

Can someone teach me or help to solve these questions using the constant difference/unchanged total method ? Thanks a lot ! :oops:


3)\tKelly had 40% as much money as Mandy. After Mandy spent $66 on a dress, the percentage of Kelly’s money increased to 60%. How much money did Kelly have?

The question is ambiguous on the 60%. The second sentence can mean :
1)- After Mandy spent $66 on a dress, the percentage of Kelly’s money increased to 60% of Mandy's money.

OR

2) After Mandy spent $66 on a dress, the percentage of Kelly’s money increased to 60% of total amount they had.

Going with the flow of the question, I am assuming the question refers to (1) above.

At first,
Kelly's money : Mandy's money = 4 : 10 = 2 : 5 --> 6u : 15u

In the end,
Kelly's money : Mandys money = 6:10 --> 6u : 10u

Amount Mandy spent = 15u - 10u = 5u --> $66
1u --> $13.20

Kelly's money --> 6 x $13.20 = $79.20

cheers.

[MathIzzzFun]

zombie:

Can someone teach me or help to solve these questions using the constant difference/unchanged total method ? Thanks a lot ! :oops:


4)\tAiling has 10% more money than Belle and Belie has 25% more money than Cally. If Ailing has $78 more than Cally, how much do the three of them have?

Ailing : Belle = 110 : 100 = 11:10
Belle : Cally = 125 : 100 = 5 : 4 = 10 : 8

Ailing : Belle : Cally --> 11u : 10u : 8u --- total --> 29u

Ailling had $78 more than Cally,
11u - 8u = 3u --> $78
1u --> $26

Total amount they had --> $26 x 29 = $754

cheers.

[MathIzzzFun]

zombie:

Can someone teach me or help to solve these questions using the constant difference/unchanged total method ? Thanks a lot ! :oops:


6)\tLucas drank 45% of a bottle of pepsi. If he drank another 1 35m1, he would have drank 75% of it. How much pepsi was there in the bottle at first?

75% - 45% = 30%
30% --> 135 ml
100% --> 450 ml

cheers.

[MathIzzzFun]

zombie:

Can someone teach me or help to solve these questions using the constant difference/unchanged total method ? Thanks a lot ! :oops:


8)\tAnne, Ben and Chris shared the cost of their seafood dinner. Anne paid 40% the total amount and Ben paid 30% of what Anne and Chris paid. If Ben paid $36 less than Chris, how much did Anne pay?

Amount paid by
Ben: Anne + Chris = 3:10 --> Ben : Anne+Ben+Chris = 3 : 13 --> 30u : 130u

Amount paid by
Anne : Anne+Ben+Chris = 4 : 10 -->52u : 130u

Amount paid by Chris --> 130u - 30u - 52u = 48u

Ben paid $36 less than Chris, so
48u-30u = 18u --> $36
1u --> $2

Anne paid --> 52 x $2 = $104

cheers.

[MathIzzzFun]

zombie:

Can someone teach me or help to solve these questions using the constant difference/unchanged total method ? Thanks a lot ! :oops:


7)\tMr Low had 40% more cows than sheep. After he sold 375 cows and bought 375 sheep, he had 80% lesser cows than sheep. How many sheep did he have in the end?

Total number of cows and sheep remain the same.
At first, cows : sheep = 140 : 100 --> 7u : 5u
In the end, cows : sheep = 20 : 100 --> 2u : 10u
7u-2u = 5u --> 375
1u --> 75
Number of sheep in the end --> 750

cheers.

[jewelbox]

Hi, how do i solve this qn. My ans of 500 is wrong. Ans given is 494.4 min. Thanks. http://i45.tinypic.com/2ykjfcw.jpg\">