Q&A - PSLE Math

[MathIzzzFun]

susutoo:

hi,

sorry forget to attached image
http://i45.tinypic.com/nqusdd.jpg\">

alternate approach :

fill in the unshaded with the area of quadrants and semi circle
--> 3/4 x 22/7 x7 x7 = 115.5 cm2

Total area of the rectangle = 115.5 + 91.5 = 207 cm2

The breadth and length of the card are whole numbers
--> 207 = 23 x 9

perimeter of rectangular card = (23+9) x 2 = 64 cm

cheers.

[charsen]

verykiasumummy:

hi charsen,


r u a tutor or teacher?

Refer to your Private Im just a psle student. Pls bear with any wrong answers ad im also learning.

[tianzhu]

Winx5015:

Hi, please help !


http://i46.tinypic.com/r1m0k5.jpg\">

Hi

b) 8 grey, 56 white

c) figure 14

Best wishes

[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.