Multiplying and Dividing Fractions

How do we write the number 3 as a fraction?

Answer explanation

 $\frac{3}{1}\ is\ the\ answer$  

 $\frac{1}{2}\ x\ 2$  

 $3\ x\ \frac{1}{2}$  

 $\frac{1}{2}\ x\ \frac{1}{2}$  

 $\frac{3}{4}\ x\ \frac{1}{4}$  

Do we need to find a common denominator when multiplying or dividing fractions?

 $\frac{2}{5}\ x\ \frac{1}{4}$  

 $\frac{3}{4}\ x\ \frac{3}{5}$  

 $1\frac{2}{3}\ x\ \frac{2}{7}$  

 $3\frac{1}{4}\ x\ \ 2\frac{1}{3}$