Q&A - PSLE Math

[sushi88]

Hi, Can someone please help with this question ? Tks in adv !

$10--(-u-)
$2---(-u-)(52)

10u -> 2(u+52)
10u -> 2u+104
8u-> 104
u-> 13

Hence MP3 player cost $10x13 = $130

Check: 2 x (13+52) = 2 x 65 = 130.

[Ender]

Hi, Can someone please help with this question ? Tks in adv !

This is essentially a large circle of radius 28 cm with 2 smaller circles inside it with radius 14cm.
Area of shaded area
= area of large circle - area of 2 small circles
= pi(28)(28) - 2pi(14)(14)
= pi(784-392)
= 392pi cm2

Perimeter of one shaded region
= Perimeter of quadrant + perimeter of semi-circle
= 2pi(28)/4 + 2pi(14)/2
= 28pi cm

Perimeter of 4 shaded region
= 4 x 28pi
= 112pi cm

I'm of the opinion that we should add on the vertical straight lines of the quadrants too for the perimeter,
Making the perimeter = 112pi + 112

[Jerico]

sushi88 and Ender for your help !

[sushi88]

I'm of the opinion that we should add on the vertical straight lines of the quadrants too for the perimeter,
Making the perimeter = 112pi + 112

Yes you are right, Ender!
I broke down the barriers for area and forgot to put back the boundaries for perimeter.
Use abstract thinking and forget the eyes...

You are welcome, Jerico.

[alfretztay]

very much alfretztay for your detailed explanation. Understand it more clearly now.

You are most welcome, EC72; and I am glad that you are able to understand.

[EC72]

This year, there are 2300 pupils in Sentosa Primary School. Comparing to last year, there is a 25% increase in the number of boys and a 25% decrease in the number of girls. The total number of students this year has increased by 15%.


a) Find the total number of pupils in Sentosa Primary School last year. (Got the answer as 2000)
b) Find the number of boys in the school this year.

[EC72]

Mrs. Lim bought some white rice and some brown rice. She cooked an equal amount of white and brown rice. She had 3/4 of the white rice and 3/8 of the brown rice left. What fraction of the rice which Mrs. Lim bought was cooked?

[EC72]

Khalid has two rectangular boxes of different sizes. The length, breadth and height of the larger box are twice those of the smaller box.

He packed 24 identical cubes exactly into the smaller box. How many such cubes can be packed exactly into the larger box?

[Ender]

This year, there are 2300 pupils in Sentosa Primary School. Comparing to last year, there is a 25% increase in the number of boys and a 25% decrease in the number of girls. The total number of students this year has increased by 15%.


a) Find the total number of pupils in Sentosa Primary School last year. (Got the answer as 2000)
b) Find the number of boys in the school this year.

Let last years number of boys be 4B and girls be 4G
Last year number of pupils is 2300/1.15 =2000

4B + 4G = 2000 => 12B + 12G = 6000 --(1)
5B + 3G = 2300 => 20B + 12G = 9200 ---(2)

(2) - (1)
8B = 3200
B= 400

This year, boys = 5B= 2000

[EC72]

This year, there are 2300 pupils in Sentosa Primary School. Comparing to last year, there is a 25% increase in the number of boys and a 25% decrease in the number of girls. The total number of students this year has increased by 15%.


a) Find the total number of pupils in Sentosa Primary School last year. (Got the answer as 2000)
b) Find the number of boys in the school this year.

Let last years number of boys be 4B and girls be 4G
Last year number of pupils is 2300/1.15 =2000

4B + 4G = 2000 => 12B + 12G = 6000 --(1)
5B + 3G = 2300 => 20B + 12G = 9200 ---(2)

(2) - (1)
8B = 3200
B= 400

This year, boys = 5B= 2000

Ender!