Q&A - PSLE Math

[jewelbox]

Zeemimi, thanks for the solution. You present it very clearly.

[kwcllf]

Hi,


Please help:

1+3+6+10+15+21+28+36+45+55..........

For such as a sequence, what is the formula to calculate the Sum of all the numbers.

Thanks.

[tianzhu]

kwcllf:

Hi,


Please help:

1+3+6+10+15+21+28+36+45+55..........

For such as a sequence, what is the formula to calculate the Sum of all the numbers.

Thanks.

Hi

You may find lots of information on triangular numbers by doing a google search.

Do a search by typing \"sum of triangular numbers\".

Best wishes

[tianzhu]

zanen:

hello can help me with this qns 10 workers can complete a painting job. If there are 2 more workers, the painting job will be completed 6 days sooner. If the same painting job were to be done 21 days earlier, how many additional workers are needed?

Hi

Please refer to charsen's solution.

Best wishes

[Winx5015]

Hi, can anyone help me with this question?



http://i48.tinypic.com/35mf6gn.jpg\">


:thankyou:

[Winx5015]

Hello, please help me with the following questions.


(1). Ali, Ben and Carl weighed themselves using a defective bathroom scale. The average mass of the 3 boys was 72.6kg. Given that Ben is 2/3 of Ali’s mass and Carl is 4/5 of Ben’s mass, what is Carl’s actual mass?

(2). The distance between Town A and Town B is 116km. A bus left Town A and headed for Town B. Some time later, a car left Town A and headed for Town B along the same route. Along the way, the car overtook the bus and arrived at Town B 45 minutes earlier than the bus. When the car arrived at Town B, the bus had travelled 5/8 of the distance. What was the speed of the bus?

(3). Tank A measures 30cm by 20cm by 24cm. It contains 12 600cm cube of water. Tank B has a square base of length 25cm and is filled with water up to a height of 11.2cm. The water in Tank A is then poured into Tank B until the water levels in both tanks are the same.
(a). What is the water level in Tank B at the end?
(b). Water is then poured from Tank B back into Tank A such that the water level in Tank A is 1.5 times the water level in Tank B. What is the water level in Tank A? Give your answer, correct to 2 decimal places.

Thanks!

[tianzhu]

Winx5015:

Hi, can anyone help me with this question?



http://i48.tinypic.com/35mf6gn.jpg\">


:thankyou:

Hi

Use the formula for circumference of circle.

1)Perimeter for 2/9 of circle (80 degrees) of radius 7 cm------- 2/9*2*pi*7

2)Perimeter for 7/9 of circle (280 degrees) of radius 3 cm------- 7/9*2*pi*3

AE = CG =BF = DH -------- 7-3 ----- 4

4*4 ------- 16

Add 16cm to the the answers found in (1) and (2)

You should get 40.4 cm.

Best wishes

[tianzhu]

Winx5015:

(2). The distance between Town A and Town B is 116km. A bus left Town A and headed for Town B. Some time later, a car left Town A and headed for Town B along the same route. Along the way, the car overtook the bus and arrived at Town B 45 minutes earlier than the bus. When the car arrived at Town B, the bus had travelled 5/8 of the distance. What was the speed of the bus?

Hi

For Speed question, it’s useful to start with a simple diagram.

116/8 ------ 14.5

14.5*3 ------- 43.5

Speed of bus ------- 43.5*(4/3) -------58 km/h

Best wishes

[tianzhu]

Winx5015:

(1). Ali, Ben and Carl weighed themselves using a defective bathroom scale. The average mass of the 3 boys was 72.6kg. Given that Ben is 2/3 of Ali's mass and Carl is 4/5 of Ben's mass, what is Carl's actual mass?

Hi

Please check your source.

I think some information might be missing.

Best wishes

[tianzhu]

Winx5015:

(3). Tank A measures 30cm by 20cm by 24cm. It contains 12 600cm cube of water. Tank B has a square base of length 25cm and is filled with water up to a height of 11.2cm. The water in Tank A is then poured into Tank B until the water levels in both tanks are the same.
(a). What is the water level in Tank B at the end?
(b). Water is then poured from Tank B back into Tank A such that the water level in Tank A is 1.5 times the water level in Tank B. What is the water level in Tank A? Give your answer, correct to 2 decimal places.

Hi

Tank A

Area -------- 600 (30*20)

Volume -------- 12600

Tank B

Area -------- 625 (25*25)

Volume -------- 7000 (625*11.2)

Total volume ------- 19600

Total base areas ------- 1225

(a)Height ------- 19600/1225 ------- 16

Tank A ------ 3 units

Tank B ------- 2 units

3 units *600 + 2 units*625 ------- 19600

Therefore 3 units ------- 19.28

Best wishes