Calculate the expansion number and the numerator.

First, calculate the expansion number by dividing the two denominators.

Second, calculate the numerator by multiplying it with the expansion number.

If you would like to have a vivid explanation with a detailed example, please read the page Expanding Fractions - The cake must be enough for everyone

**Step 1: Calculate the Expansion Number**

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To calculate the *expansion number*, divide the denominator of the expanded fraction () by the denominator of the first fraction (1):

Expansion Number = 21 ÷ 7 = 3

**Step 2: Calculate the numerator**

To calculate the *numerator* of the second fraction, multiply the numerator of the first fraction (7) by the expansion number (3):

Numerator = 1 × 3 = 3