Question

The product of a number and 50

Answer 1

"Product" means we are looking at a multiplication problem.

Can be written as: 

A number (n) times 50

n x 50

The simplest (and most common way) to write it:

50n

Answer 2

product means multiplcation
product of x and y means x times y or xy
like sum of x and y=x+y so


a number could be any number, we will represent it as x so
product of x and 50=x50 or 50x