The average number of mangosteens in Box A, Box B and Box C is 20 and it is 5 more than the average number of chikoos in the 3 boxes. ¹₅ of the chikoos are in Box A and the chikoos in Box A is 60% of the number of chikoos in Box B. If each box has the same number of fruits, what percentage of the fruits in Box C are mangosteens?
Average number of chikoos
= 20 - 5
= 15

Total number of chikoos
= 3 x 15
= 45

Total number of mangosteens
= 3 x 20 
= 60

Total number of fruits
= 45 + 60
= 105

Number of fruits in each box
= 105 ÷ 3
= 35

Chikoos in Box A	Chikoos in Box B	Chikoos in Box C	Total chikoos
1x3	4x3		5x3
3x1	5x1
3 u	5 u	7 u	15 u

60% = ⁶⁰₁₀₀ = ³₅

The number of chikoos in Box A is repeated.  Make the number of chikoos in Box A the same.  LCM of 1 and 3 is 3. 

Total number of chikoos
= 3 u + 5 u + 7 u
= 15 u

15 u = 45

1 u = 45 ÷ 15 = 3

Number of chikoos in Box C
= 7 u
= 7 x 3
= 21

Number of mangosteens in Box C
= 35 - 21
= 14

Percentage of the fruits in Box C are mangosteens
= ¹⁴₃₅ x 100%
= 40%

Answer(s): 40%