Answer:
15 batteries
Step-by-step explanation:
If he puts the batteries in piles of 4, and there is 3 left over, the number of batteries he can have is:
2 piles: 4*2 + 3 = 11
3 piles: 4*3 + 3 = 15
4 piles: 4*4 + 3 = 19
Then, when he puts in piles of 3, there is no batteries left over, so the number of batteries is a multiple of 3.
From the 3 possibilities above (11, 15 and 19), only the number 15 is a multiple of 3, so the number of batteries is 15.
