The average height of a starfruit tree, a mango tree and a mangosteen tree is 4.6 m. The mangosteen tree is twice as tall as the mango tree and 1.2 m taller than the starfruit tree. Find the average height of the starfruit tree and the mango tree.
Total height of the starfruit tree, the mango tree and the mangosteen tree
= 3 x 4.6
= 13.8 m

Height of the mango tree = 1 u
Height of the mangosteen tree = 2 u
Height of the starfruit tree = 2 u - 1.2

Total height of the starfruit tree, the mango tree and the mangosteen tree
= 1 u + 2 u + 2 u - 1.2
= 5 u - 1.2

5 u - 1.2 = 13.8
5 u = 13.8 + 1.2
5 u = 15

1 u = 15 ÷ 5 = 3

Total height of the starfruit tree and the mango tree
= 1 u + 2 u - 1.2
= 3 u - 1.2
= 3 x 3 - 1.2
= 9 - 1.2
= 7.8 m

Average height of the starfruit tree and the mango tree
= 7.8 ÷ 2
= 3.9 m

Answer(s): 3.9 m