Question

Bob uses $3$ cups of sugar for every $5$ cups of flour to bake a cake. How many cups of sugar will he use if he uses $20$ cups of flour?

• A. $20$
• B. $12$
• C. $8$
• D. $15$

Answer 1

The correct option is B $12$

For every $5$ cups of flour, $3$ cups of sugar are needed.
Ratio of sugar to flour $=3:5$
Number of cups of flour used for the cake $=20$
Let’s assume Bob uses $n$ cups of sugar to bake the cake.

The ratio of the number of cups of flour to the number of cups of sugar will be in proportion.
Hence, $3:5::n:20$
The ratio on the $RHS$ is an equivalent ratio of $3:5$.
$\Rightarrow \frac{3}{5}=\frac{n}{20}$
$\Rightarrow n\times 5=3\times 20$
$\Rightarrow n\times 5=60$
$\Rightarrow n=\frac{60}{5}=12$
Hence, $12$ cups of sugar will be required for $20$ cups of flour.