The average height of a mangosteen tree, a starfruit tree and a coconut tree is 5.6 m. The coconut tree is four times as tall as the starfruit tree and 1.2 m taller than the mangosteen tree. Find the average height of the mangosteen tree and the starfruit tree.
Total height of the mangosteen tree, the starfruit tree and the coconut tree
= 3 x 5.6
= 16.8 m

Height of the starfruit tree = 1 u
Height of the coconut tree = 4 u
Height of the mangosteen tree = 4 u - 1.2

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

9 u - 1.2 = 16.8
9 u = 16.8 + 1.2
9 u = 18

1 u = 18 ÷ 9 = 2

Total height of the mangosteen tree and the starfruit tree
= 1 u + 4 u - 1.2
= 5 u - 1.2
= 5 x 2 - 1.2
= 10 - 1.2
= 8.8 m

Average height of the mangosteen tree and the starfruit tree
= 8.8 ÷ 2
= 4.4 m

Answer(s): 4.4 m