Tashia ate 1/3 of a pizza, and jay ate 3/8 of the same pizza. what fraction of the pizza was eaten?

This is basically saying how much of the pizza did Tashia and Jay both ate, thus combining their portions together.

1/3 + 3/8 = fraction of pizza eaten

To add fractions, you must have a common denominator. Which is 24 in this case because 3*8 = 24.

So you multiply 1/3 with 8 and multiply 3/8 with 3.

1/3*8= 8/24
3/8*3= 9/24

Now you add the fractions.
8/24+9/24= 17/24. You add the numerator, the denominator stays the same.

17/24 of the pizza was eaten.