Question

find all the factor pairs for 21 and complete the equations.
21 = \square \cdot 21
21 = 3 \cdot \square

Explanation:

Step1: Find first missing factor

To find the number that multiplies by 21 to get 21, divide 21 by 21:
$\frac{21}{21}=1$

Step2: Find second missing factor

To find the number that multiplies by 3 to get 21, divide 21 by 3:
$\frac{21}{3}=7$

Answer:

$21 = 1 \cdot 21$
$21 = 3 \cdot 7$
The full factor pairs of 21 are (1, 21) and (3, 7)