If $\dfrac{x}{49} = \dfrac{3}{21}$, what is the value of $x$?

Question

Accepted Answer

B. $7$

Cross-multiply: $21x = (3)(49) = 147$.
Divide both sides by $21$: $x = \dfrac{147}{21} = 7$.
Check: $\dfrac{7}{49} = \dfrac{1}{7}$ and $\dfrac{3}{21} = \dfrac{1}{7}$ ✓.
Shortcut: $\dfrac{3}{21} = \dfrac{1}{7}$, so $\dfrac{x}{49} = \dfrac{1}{7}$, giving $x = 49/7 = 7$.
- Trap C ($14$) misreads the ratio.
- Trap D ($21$) confuses the numerator with the denominator of the right-hand fraction.

Answer

$3$

Answer

$14$

Answer

$21$