The average height of a coconut tree, a mango tree and a mangosteen tree is 6.6 m. The mangosteen tree is thrice as tall as the mango tree and 1.2 m taller than the coconut tree. Find the average height of the coconut tree and the mango tree.
Total height of the coconut tree, the mango tree and the mangosteen tree
= 3 x 6.6
= 19.8 m

Height of the mango tree = 1 u
Height of the mangosteen tree = 3 u
Height of the coconut tree = 3 u - 1.2

Total height of the coconut tree, the mango tree and the mangosteen tree
= 1 u + 3 u + 3 u - 1.2
= 7 u - 1.2

7 u - 1.2 = 19.8
7 u = 19.8 + 1.2
7 u = 21

1 u = 21 ÷ 7 = 3

Total height of the coconut tree and the mango tree
= 1 u + 3 u - 1.2
= 4 u - 1.2
= 4 x 3 - 1.2
= 12 - 1.2
= 10.8 m

Average height of the coconut tree and the mango tree
= 10.8 ÷ 2
= 5.4 m

Answer(s): 5.4 m