There were some mangosteens, apples and starfruits. The number of mangosteens was two times the number of apples. The total number of mangosteens and apples was one-third of the number of starfruits. There were 168 fruits altogether. All the starfruits were sold at 6 for $10. How much money was collected from the sale of the starfruits?
Number of apples = 1 u
Number of mangosteens = 2 u

Total number of apples and mangosteens
= 1 u + 2 u
= 3 u

Number of starfruits
= 3 x 3 u
= 9 u

Total number of fruits
= 1 u + 2 u + 9 u
= 12 u

12 u = 168

1 u = 168 ÷ 12 = 14

Number of starfruits sold
= 9 u
= 9 x 14
= 126

Number of sets of 6 starfruits
= 126 ÷ 6
= 21

Amount collected from the sale of starfruits
= 21 x 10
= $210

Answer(s): $210