The average height of a durian tree, a mangosteen tree and a mango tree is 6.2 m. The mango tree is twice as tall as the mangosteen tree and 1.4 m taller than the durian tree. Find the average height of the durian tree and the mangosteen tree.
Total height of the durian tree, the mangosteen tree and the mango tree
= 3 x 6.2
= 18.6 m

Height of the mangosteen tree = 1 u
Height of the mango tree = 2 u
Height of the durian tree = 2 u - 1.4

Total height of the durian tree, the mangosteen tree and the mango tree
= 1 u + 2 u + 2 u - 1.4
= 5 u - 1.4

5 u - 1.4 = 18.6
5 u = 18.6 + 1.4
5 u = 20

1 u = 20 ÷ 5 = 4

Total height of the durian tree and the mangosteen tree
= 1 u + 2 u - 1.4
= 3 u - 1.4
= 3 x 4 - 1.4
= 12 - 1.4
= 10.6 m

Average height of the durian tree and the mangosteen tree
= 10.6 ÷ 2
= 5.3 m

Answer(s): 5.3 m