During a promotional event a sporting good store gave a free t-shirt every eighth customer and a free water bottle every 10th customer which customer was the first to get a free t-shirt and a free water bottle

40th customer

Step-by-step 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.