Fraction Subtraction: Finding Remaining Pizza After 2/7 and 1/3 are Eaten

To solve this problem, we'll follow these steps:

• Step 1: Identify the total fraction consumed by Roberto and Marcelo.
• Step 2: Find a common denominator to add these fractions.
• Step 3: Subtract the total consumed from the whole pizza.

Let's work through each step:

Step 1: Roberto eats $\frac{2}{7}$ of the pizza, and Marcelo eats $\frac{1}{3}$.

Step 2: To add these fractions, we need a common denominator. The least common denominator between 7 and 3 is 21.

Convert the fractions:
Roberto's fraction: $\frac{2}{7} = \frac{2 \times 3}{7 \times 3} = \frac{6}{21}$
Marcelo's fraction: $\frac{1}{3} = \frac{1 \times 7}{3 \times 7} = \frac{7}{21}$

Step 3: Add the converted fractions:
$\frac{6}{21} + \frac{7}{21} = \frac{13}{21}$

This result represents the total fraction of the pizza eaten by Roberto and Marcelo.

Step 4: Subtract the eaten fraction from the whole pizza (1, or $\frac{21}{21}$):
$\frac{21}{21} - \frac{13}{21} = \frac{8}{21}$

Therefore, the amount of pizza left for Diego to eat is $\frac{8}{21}$.