Matching a formula to a given context

Matching a formula to a given context

Question 1

John is 3 years younger than Mary. Which statement is correct?
	a	Mary's age + John's age = 3.
	b	Mary's age = John's age + 3.
	c	John's age − Mary's age = 3.
	d	John's age = Mary's age + 3.

Solution (forming an equation)

John's age = Mary's age − 3.

Rearrange the equation.

John's age + 3 = Mary's age.

This shows the statements 'John is 3 years younger than Mary' and 'Mary is 3 years older than John' are equivalent.

Mary's age = John's age + 3. This is option b.

Check the answer for a special case. For example:

If John is 10 years old, Mary would be 13 years old.

Solution (substituting values)