I: 0

II: 9

Range = 2

There are several sets wirh range 2 and min max number pairs as: (1,3) (2,4), (3,5).....

Set1: (2,4) i.e, Set with min = 2 and max = 4 can have, 0 students contributing 3.

x=number of contributing 2

y= number of people contributing 4

2x+4y = 28

x+y = 10

=> x = 6 & y = 4

So there can be 0 boys contributing 3.

(I: 0 is POSSIBLE)
Set2: (1,3)

x = number of contributing 1

y = number of people contributing 3

x + 3y = 28

x + y = 10

=> x = 1, y=9

Therefor 9 boys can be contributing 3

(III: 9 is POSSIBLE)
Others don't satisfy all the three conditions.

What's the source joemama. I had to scratch my head several times and still I am not sure about the answer

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