Q&A - PSLE Math

[questionable_i]

Sorry, I need help with this question again.

once again.

[Laurel111]

Can someone please help.

[Ender]

Area of quandrant DXC = π X 18 X 18 /4 = 81π cm²
Area of Triangle AXB = 1/2 X 18 X 9 = 81 cm²
Area of semi circle AB = π X 9 X 9 /2 = 40.5π cm²

Shade area = 2 X (81π - 40.5π - 81)
= 81π -162 cm²

[Ender]

Sorry, I need help with this question again.

once again.

For multiple choice, you have to learn to eliminate the obvious to save time.
a quick calculation say 25% of 220 = 55

He want to add on til 45%. Means the new total will be increased. 25% of the new total is definately more than 55. Therefore we can eliminate choice 1) and 2)

Let's check choice 3) Increase by 80
New total = 300
New Singapore stamps = 55 + 80 =135
Check percentage = 135/300 X 100 = 45% ## bingo..

____________________________________
And the math if you decide to do this way,
(55 + u)/(220+u) = 0.45
55+u = 99 + 0.45u
44 = 0.55u
u = 80 ###

[Laurel111]

Thank you Ender

[Nebbermind]

Area of quandrant DXC = π X 18 X 18 /4 = 81π cm²
Area of Triangle AXB = 1/2 X 18 X 9 = 81 cm²
Area of semi circle AB = π X 9 X 9 /2 = 40.5π cm²

Shade area = 2 X (81π - 40.5π - 81)
= 81π -162 cm²

Alternatively, you cut the big semi circle into half.
The area of shaded part is 1/4 of the big circle minus one small circle.

[Nebbermind]

Can anyone help me with this question?

Let number of tin at first be u

20 X u = 16 X (u+5)
20u = 16u + 80
4u = 80
u = 20 ###

Alternatively, if each of the remaining 16 shelves increase by 5 tins,
then total tins removed from the four shelves = 16 x 5 = 80

Therefore there were originally 80/4, ie, 20 on each shelves

[Ender]

Area of quandrant DXC = π X 18 X 18 /4 = 81π cm²
Area of Triangle AXB = 1/2 X 18 X 9 = 81 cm²
Area of semi circle AB = π X 9 X 9 /2 = 40.5π cm²

Shade area = 2 X (81π - 40.5π - 81)
= 81π -162 cm²

Alternatively, you cut the big semi circle into half.
The area of shaded part is 1/4 of the big circle minus one small circle.

Area of big quadrant = 81pi
Area of small circle = 81 pi

81pi - 81pi = 0???

[Nebbermind]

Area of quandrant DXC = π X 18 X 18 /4 = 81π cm²
Area of Triangle AXB = 1/2 X 18 X 9 = 81 cm²
Area of semi circle AB = π X 9 X 9 /2 = 40.5π cm²

Shade area = 2 X (81π - 40.5π - 81)
= 81π -162 cm²

Alternatively, you cut the big semi circle into half.
The area of shaded part is 1/4 of the big circle minus one small circle.

Area of big quadrant = 81pi
Area of small circle = 81 pi

81pi - 81pi = 0???

Oops. My mistake

[muska]

​Dominic has some stamps
​
​If he packs 5 stamps ​into each bag, he will have 2 extra stamps

​If he packs 8 stamps into each bag , he will need 3 more stamps

​What is the least no. of stamps dominic has?
​

Ans: 37

-How to do the question without guess n check?