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## Wednesday, September 07, 2011

### Hokkien Huay Kuan Combined Primary 2010 PSLE Math Prelim Paper 2 Q18

The figure below shows 2 completely-filled tanks being emptied of the water from 2 different taps. The taps at Tank A and Tank B were turned on at 7 am and 8.30 am respectively, until both tanks were completely empty. At 11 am, the water level in both the tanks was the same. At 12.30 pm, Tank B was completely empty and Tank A was only completely empty at 1 pm. If the rate of the flow of water from each tap was constant throughout, what was the height of Tank A?

Solution ** At 11 am, water level in both Tanks were the same.

Note that 3/8 of B's height is the same as 2/6 or 1/3 of A's height.

(3/8) of B ----- (2/6) or (1/3) of A

(1/8) of B ----- (1/3) of A divided 3 = (1/9) of A

(8/8) of B (B's height) ----- 8 x (1/9) = (8/9) of A

* Remaining (1/9) of A ----- 5 cm
(This is the difference in height between Tank A and B)

(9/9) of A (A's height) ----- 9 x 5cm = 45 cm

Answer: 45 cm

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#### 3 comments: Madhu said...

How are you able to draw such a diagram with accuracy.What clue is given in the question for you to draw the diagram.Please help.thanks

ExcelEduservice said...

There’s no need to draw accurately. I drew it for easy illustration.

Important thing is to know that at 11am 2/3 of Tank A has been drained and 5/8 of Tank B has been drained. This means that 1/3 of the remaining level in Tank A is the same as 3/8 of the level in Tank B.

Therefore, 1/3 of Tank A is equal to 3/8 of Tank B. We also know that Tank B is shorter than Tank A by 5 cm.

From here, we can carry on the same calculation as illustrated in the main post. Which is,

(3/8) of B ----- (2/6) or (1/3) of A

(1/8) of B ----- (1/3) of A divided 3 = (1/9) of A

(8/8) of B (B's height) ----- 8 x (1/9) = (8/9) of A

* Remaining (1/9) of A ----- 5 cm
(This is the difference in height between Tank A and B)

(9/9) of A (A's height) ----- 9 x 5cm = 45 cm

Answer: 45 cm Madhu said...

Thank you very much for the explanation.i now have a clearer understanding.