Answer:
40th customer
Explanation:
Given that there is a promotional event
A sporting good store gave t shirt and free water bottle.
T shirt was given to 8th customer and water bottle to every 10th customer.
For the first person who should get both, he should have number as least common multiple of 8 and 10
8 = 2x2x2
10 = 2x5
Hence least common denominator = 2x2x2x5 = 40
Thus 40th customer will be the first to get both.