PSLE
There was a total of 13724 cm³ of water in rectangular tanks N and P at first. The height of the water level in tank P was 3 cm above that of tank N.

1. Find the height of the water level in tank N.
2. Sarah poured 3840 cm³ of water out of tank P. Tank P was then half filled with water. What was the height of tank P?

(a)
Volume of water in Tank P with a height of 3 cm
= 32 x 24 x 3
= 2304 cm³

Volume of water in both tanks excluding the water that is 3 cm above that of Tank N
= 13724 - 2304
= 11420 cm³

Base area of Tank N
= 22 x 17
= 374 cm²

Base area of Tank P
= 32 x 24
= 768 cm²

Combined base areas of both tanks
= 374 + 768
= 1142 cm²

Height of water in Tank N 
= 11420 ÷ 1142
= 10 cm

(b)
Decrease in the height of Tank P after some water was poured out 
= 3840 ÷ 768
= 5 cm

Original height of water before some was poured out
= 10 + 3
= 13 cm

Height of water after some was poured out
= 13 - 5
= 8 cm

Height of Tank N
= 2 x 8
= 16 cm

Answer(s): (a) 10 cm; (b) 16 cm