Question

A biscuit recipe calls for 3 2/3 cups of flour for 1 batch. How many cups are needed for 3 1/4 batches?

Answer 1

Multiply 3.6666 by 3.25 to get 11.9167 cups. 

Answer 2

This problem can be solved easily using a proportion:
$3\frac{2}{3} - 1$
$x - 3\frac{1}{4}$

So, $x= \frac{3\frac{2}{3} * 3\frac{1}{4}}{1}=3\frac{2}{3} * 3\frac{1}{4}=\frac{11}{3} * \frac{13}{4}=\frac{11*13}{3*4}=\frac{143}{12}=11\frac{11}{12}$

The answer:  $11\frac{11}{12}$ cups are needed.