PSLE
There was a total of 26730 cm³ of water in rectangular tanks B and C at first. The height of the water level in tank C was 7 cm above that of tank B.

1. Find the height of the water level in tank B.
2. Jean poured 8640 cm³ of water out of tank C. Tank C was then half filled with water. What was the height of tank C?

(a)
Volume of water in Tank C with a height of 7 cm
= 36 x 30 x 7
= 7560 cm³

Volume of water in both tanks excluding the water that is 7 cm above that of Tank B
= 26730 - 7560
= 19170 cm³

Base area of Tank B
= 31 x 27
= 837 cm²

Base area of Tank C
= 36 x 30
= 1080 cm²

Combined base areas of both tanks
= 837 + 1080
= 1917 cm²

Height of water in Tank B 
= 19170 ÷ 1917
= 10 cm

(b)
Decrease in the height of Tank C after some water was poured out 
= 8640 ÷ 1080
= 8 cm

Original height of water before some was poured out
= 10 + 7
= 17 cm

Height of water after some was poured out
= 17 - 8
= 9 cm

Height of Tank B
= 2 x 9
= 18 cm

Answer(s): (a) 10 cm; (b) 18 cm