If sarah ate 1/4 of a small cupcake and becky ate 1/4 of a big cupcake did they eat the same amount

No. 1/4 of a larger amount is more than 1/4 of a smaller amount.

Imagine the small cup cake weighs 4 ounces, and the large cup cake weighs 8 ounces.

1/4 of 4 ounces = 1/4 * 4 oz = 1 oz
1/4 of 8 ounces = 1/4 * 8 oz = 2 oz

1/4 of the larger cupcake is 2 ounces, whereas 1/4 of the smaller cupcake is 1 ounce.

Even though they both ate 1/4 of a whole thing, the one who ate 1/4 of the larger thing ate more.