The average number of starfruits in Box S, Box T and Box U is 18 and it is 6 more than the average number of lemons in the 3 boxes. ¹₆ of the lemons are in Box S and the lemons in Box S is 40% of the number of lemons in Box T. If each box has the same number of fruits, what percentage of the fruits in Box U are starfruits?
Average number of lemons
= 18 - 6
= 12

Total number of lemons
= 3 x 12
= 36

Total number of starfruits
= 3 x 18 
= 54

Total number of fruits
= 36 + 54
= 90

Number of fruits in each box
= 90 ÷ 3
= 30

Lemons in Box S	Lemons in Box T	Lemons in Box U	Total lemons
1x2	5x2		6x2
2x1	5x1
2 u	5 u	5 u	12 u

40% = ⁴⁰₁₀₀ = ²₅

The number of lemons in Box S is repeated.  Make the number of lemons in Box S the same.  LCM of 1 and 2 is 2. 

Total number of lemons
= 2 u + 5 u + 5 u
= 12 u

12 u = 36

1 u = 36 ÷ 12 = 3

Number of lemons in Box U
= 5 u
= 5 x 3
= 15

Number of starfruits in Box U
= 30 - 15
= 15

Percentage of the fruits in Box U are starfruits
= ¹⁵₃₀ x 100%
= 50%

Answer(s): 50%