This blog is managed by Song Hock Chye, author of Improve Your Thinking Skills in Maths (P1-P3 series), which is published and distributed by EPH.

## Monday, September 14, 2009

### Raffles Girls Pri Sch 2007 PSLE Math Prelim Q40

A rectangular tank with 5 identical solid metal cubes was filled to the brim with water. Water was drained out of the tank through a tap at a rate of 2 litres per minute. It took 18 minutes for the water level to drop to the height of the metal cubes. Find the volume of the 5 metal cubes.

Solution

Volume of whole tank
60 cm x 20 cm x 40 cm = 48 000 cubic cm or 48 litres

1 min ----- 2 litres

18 min ----- 2 litres x 18 = 36 litres

Volume of tank filled with water + volume of cubes after 18 min
48 litres – 36 litres = 12 litres or 12 000 cm

Height of cubes is therefore,
Height ------ Volume divided by base area
= 12 000 cubic cm divided by (60 cm x 20 cm) = 10 cm

Height of cube ------ 10 cm
Volume of 1 cube ----- 10 cm x 10 cm x 10 cm = 1000 cubic cm
Volume of 5 cubes ----- 1000 cubic cm x 5 = 5000 cubic cm