Solve using the guess-and-check strategy.
matthew and elizabeth have a combined age of 19 years. matthew is 5 years older than elizabeth. how old is matthew?
a. 7
b. 8
c. 12
d. 26

The answer is 12. Matthew would be 12 & Elizabeth would be 7. 12+7=19. So C is your answer. 

The simplest way to do this would be to first subtract 5 from the total, because Matthew is going to be five years older than her.

19 - 5 = 14

14 will divide evenly by 2, making them each 7, but since Matthew is 5 years older, and 5 back to 7 to get his age.

7 + 5 = 12.

Matthew is 12 and Elizabeth is 7. Check your work.

12 + 7 = 19

Write checks carefully, keep and accurate record of checks, and deposits made.