Question

After the party, there was 0.5 of the pizza left. Angela ate 0.2 of the leftover pizza.

Answer 1

For one thing, Cal and Martha are technically in agreement; 0.1 and 0.10 are the exact same value. To see whether they're right, or whether Angela had it correct, let's take a look at the numbers 0.5 and 0.2.

As fractions, those two values would be $\frac{5}{10}$ and $\frac{2}{10}$, or $\frac{1}{2}$ and $\frac{1}{5}$ when reduced. When you cut the original pizza in half, you cut it into 2 equal slices. Cutting each of those two pieces into 5 equal pieces, we get a total of 5 x 2 = 10 equal slices. So, taking one of those slices at that point - as Angela did - would be taking $\frac{1}{10}$ - or 0.1 - of the whole pizza.

So, both Cal and Martha are correct.