Question

Julio's father is 4 times as old as Julio. The sum of their ages is no less than 55.

Answer 1

Call (F) the age of the father and (J) the age of Julio

The F & J are related in this way: F=4J

 Now you have a restriction in the form of inequality: The sum of both ages has to be greater or equal than 55.

Algebraically that is: F + J ≥ 55

You can substitute F with 4J to find the solution for J: 

4J + J ≥ 55

5J ≥ 55

Now divide both sides by 5

5J/5 ≥ 55/5

J ≥ 11 

That Imposes a lower boundary for the value of J of 11, meaning that the youngest age of Julio can be 11