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

Height of the guava tree = 1 u
Height of the durian tree = 3 u
Height of the starfruit tree = 3 u - 1.8

Total height of the starfruit tree, the guava tree and the durian 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 starfruit tree and the guava 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 starfruit tree and the guava tree
= 10.2 ÷ 2
= 5.1 m

Answer(s): 5.1 m