Question:
Two salesmen make equal sales during the month of August. In September, each salesman doubles his sale of the month of August. Compare their sales in September.
Solution:
Let the equal sale of two salesmen in August be $x$.
In September each salesman doubles his sale of August.
Thus, sale of first salesman is $2 x$ and sale of second salesman is $2 x$.
According to Euclid's axioms, things which are double of the same things are equal to one another.
So, in September their sales are again equal.