PSLE
There was a total of 18630 cm³ of water in rectangular tanks F and G at first. The height of the water level in tank G was 6 cm above that of tank F.

1. Find the height of the water level in tank F.
2. Rachel poured 3780 cm³ of water out of tank G. Tank G was then half filled with water. What was the height of tank G?

(a)
Volume of water in Tank G with a height of 6 cm
= 27 x 20 x 6
= 3240 cm³

Volume of water in both tanks excluding the water that is 6 cm above that of Tank F
= 18630 - 3240
= 15390 cm³

Base area of Tank F
= 18 x 15
= 270 cm²

Base area of Tank G
= 27 x 20
= 540 cm²

Combined base areas of both tanks
= 270 + 540
= 810 cm²

Height of water in Tank F 
= 15390 ÷ 810
= 19 cm

(b)
Decrease in the height of Tank G after some water was poured out 
= 3780 ÷ 540
= 7 cm

Original height of water before some was poured out
= 19 + 6
= 25 cm

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

Height of Tank F
= 2 x 18
= 36 cm

Answer(s): (a) 19 cm; (b) 36 cm