The average height of a mangosteen tree, a chikoo tree and a starfruit tree is 6.4 m. The starfruit tree is thrice as tall as the chikoo tree and 1.8 m taller than the mangosteen tree. Find the average height of the mangosteen tree and the chikoo tree.
Total height of the mangosteen tree, the chikoo tree and the starfruit tree
= 3 x 6.4
= 19.2 m

Height of the chikoo tree = 1 u
Height of the starfruit tree = 3 u
Height of the mangosteen tree = 3 u - 1.8

Total height of the mangosteen tree, the chikoo tree and the starfruit tree
= 1 u + 3 u + 3 u - 1.8
= 7 u - 1.8

7 u - 1.8 = 19.2
7 u = 19.2 + 1.8
7 u = 21

1 u = 21 ÷ 7 = 3

Total height of the mangosteen tree and the chikoo tree
= 1 u + 3 u - 1.8
= 4 u - 1.8
= 4 x 3 - 1.8
= 12 - 1.8
= 10.2 m

Average height of the mangosteen tree and the chikoo tree
= 10.2 ÷ 2
= 5.1 m

Answer(s): 5.1 m