Which is bigger two thirds or seven eights

Seven eigths, because if you divide 7/8 you get 0.875 and that is bigger  that dividing 2/3 and getting 0.3333333...

Let's compare apples to apples by finding a common denominator...

2/3
7/8

3×8 = 24 we'll use that

You multiply 3 by 8 to get 24 in the denominator, so multiply the numerator by the same amount...

2/3 × 8/8 = 16/24

Do the same with the other fraction but multiply by 3...

7/8 × 3/3 = 21/24

Now we can compare...

16/24 is less than 21/24 so 2/3 is less than 7/8.