Q&A - PSLE Math

[Winx5015]

Hi, can anyone help me with this question?



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: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?



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: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

[Winx5015]

Hi tianzhu, thanks for your help. Regarding Q(1), will check with the teacher.


Once again, thanks

[Zhu99]

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.

n(n + 1)(n +2)/6

[tianzhu]

Recia Lim:

Thanks! How do we know when should we use this inverse proportion method?

Hi

Good Morning.

I am sorry for the late response.

I am not too sure if I am in an appropriate position to answer your question since I am not actively following the school syllabus as I am a post PSLE dad.

There were some discussions in this thread in 2009 concerning the use of inverse proportion for Speed questions. The understanding I had was this inverse ratio way of tackling Speed questions was taught to selected students, probably with higher mathematical abilities. Some students may also learn this technique from their tuition classes.

If you look at the P6 books, the syllabus touches on the Speed Triangle, Distance ------ Speed*Time.

From my limited encounters with past years questions, it is good enough to solve questions with the Speed Triangle. The inverse ratio method offers an alternative.

Here's a solution to your question using the Speed Triangle.

Let the child choose the method he/she is comfortable with.

Hope this helps.

Best wishes

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[zombie]

Can someone please help me with the question ?