PSLE
There was a total of 31250 cm³ of water in rectangular tanks Q and R at first. The height of the water level in tank R was 5 cm above that of tank Q.

1. Find the height of the water level in tank Q.
2. Gwen poured 5950 cm³ of water out of tank R. Tank R was then half filled with water. What was the height of tank R?

(a)
Volume of water in Tank R with a height of 5 cm
= 34 x 25 x 5
= 4250 cm³

Volume of water in both tanks excluding the water that is 5 cm above that of Tank Q
= 31250 - 4250
= 27000 cm³

Base area of Tank Q
= 25 x 20
= 500 cm²

Base area of Tank R
= 34 x 25
= 850 cm²

Combined base areas of both tanks
= 500 + 850
= 1350 cm²

Height of water in Tank Q 
= 27000 ÷ 1350
= 20 cm

(b)
Decrease in the height of Tank R after some water was poured out 
= 5950 ÷ 850
= 7 cm

Original height of water before some was poured out
= 20 + 5
= 25 cm

Height of water after some was poured out
= 25 - 7
= 18 cm

Height of Tank Q
= 2 x 18
= 36 cm

Answer(s): (a) 20 cm; (b) 36 cm