The average height of a coconut tree, a persimmon tree and a starfruit tree is 5.4 m. The starfruit tree is four times as tall as the persimmon tree and 1.8 m taller than the coconut tree. Find the average height of the coconut tree and the persimmon tree.
Total height of the coconut tree, the persimmon tree and the starfruit tree
= 3 x 5.4
= 16.2 m

Height of the persimmon tree = 1 u
Height of the starfruit tree = 4 u
Height of the coconut tree = 4 u - 1.8

Total height of the coconut tree, the persimmon tree and the starfruit tree
= 1 u + 4 u + 4 u - 1.8
= 9 u - 1.8

9 u - 1.8 = 16.2
9 u = 16.2 + 1.8
9 u = 18

1 u = 18 ÷ 9 = 2

Total height of the coconut tree and the persimmon tree
= 1 u + 4 u - 1.8
= 5 u - 1.8
= 5 x 2 - 1.8
= 10 - 1.8
= 8.2 m

Average height of the coconut tree and the persimmon tree
= 8.2 ÷ 2
= 4.1 m

Answer(s): 4.1 m