The average number of kiwis in Box X, Box Y and Box Z is 16 and it is 8 more than the average number of starfruits in the 3 boxes. ¹₃ of the starfruits are in Box X and the starfruits in Box X is 80% of the number of starfruits in Box Y. If each box has the same number of fruits, what percentage of the fruits in Box Z are kiwis?
Average number of starfruits
= 16 - 8
= 8

Total number of starfruits
= 3 x 8
= 24

Total number of kiwis
= 3 x 16 
= 48

Total number of fruits
= 24 + 48
= 72

Number of fruits in each box
= 72 ÷ 3
= 24

Starfruits in Box X	Starfruits in Box Y	Starfruits in Box Z	Total starfruits
1x4	2x4		3x4
4x1	5x1
4 u	5 u	3 u	12 u

80% = ⁸⁰₁₀₀ = ⁴₅

The number of starfruits in Box X is repeated.  Make the number of starfruits in Box X the same.  LCM of 1 and 4 is 4. 

Total number of starfruits
= 4 u + 5 u + 3 u
= 12 u

12 u = 24

1 u = 24 ÷ 12 = 2

Number of starfruits in Box Z
= 3 u
= 3 x 2
= 6

Number of kiwis in Box Z
= 24 - 6
= 18

Percentage of the fruits in Box Z are kiwis
= ¹⁸₂₄ x 100%
= 75%

Answer(s): 75%