The average height of a durian tree, a jackfruit tree and a starfruit tree is 11.6 m. The starfruit tree is four times as tall as the jackfruit tree and 1.2 m taller than the durian tree. Find the average height of the durian tree and the jackfruit tree.
Total height of the durian tree, the jackfruit tree and the starfruit tree
= 3 x 11.6
= 34.8 m

Height of the jackfruit tree = 1 u
Height of the starfruit tree = 4 u
Height of the durian tree = 4 u - 1.2

Total height of the durian tree, the jackfruit tree and the starfruit tree
= 1 u + 4 u + 4 u - 1.2
= 9 u - 1.2

9 u - 1.2 = 34.8
9 u = 34.8 + 1.2
9 u = 36

1 u = 36 ÷ 9 = 4

Total height of the durian tree and the jackfruit tree
= 1 u + 4 u - 1.2
= 5 u - 1.2
= 5 x 4 - 1.2
= 20 - 1.2
= 18.8 m

Average height of the durian tree and the jackfruit tree
= 18.8 ÷ 2
= 9.4 m

Answer(s): 9.4 m