If he packs 5, he will be short of 4
Multiples of 5 : 5 , 10 , 15 , 20 , 25 , 30
short of 4 (-4) : 1 , 06 , 11 , 16 , 21 , 26
If he packs 4, he will have 3 left
Multiples of 4 : 4 , 08 , 12 , 16, 20 , 24
3 left (+3) : 7 , 11 , 15, 19 , 23 , 27
He has 11 apples.
