PSLE
There was a total of 33920 cm³ of water in rectangular tanks C and D at first. The height of the water level in tank D was 4 cm above that of tank C.

1. Find the height of the water level in tank C.
2. Diana poured 5580 cm³ of water out of tank D. Tank D was then half filled with water. What was the height of tank D?

(a)
Volume of water in Tank D with a height of 4 cm
= 36 x 31 x 4
= 4464 cm³

Volume of water in both tanks excluding the water that is 4 cm above that of Tank C
= 33920 - 4464
= 29456 cm³

Base area of Tank C
= 29 x 25
= 725 cm²

Base area of Tank D
= 36 x 31
= 1116 cm²

Combined base areas of both tanks
= 725 + 1116
= 1841 cm²

Height of water in Tank C 
= 29456 ÷ 1841
= 16 cm

(b)
Decrease in the height of Tank D after some water was poured out 
= 5580 ÷ 1116
= 5 cm

Original height of water before some was poured out
= 16 + 4
= 20 cm

Height of water after some was poured out
= 20 - 5
= 15 cm

Height of Tank C
= 2 x 15
= 30 cm

Answer(s): (a) 16 cm; (b) 30 cm