Question posted by Kelvin and Jeanie from Singapore:

Fred saves \$90 more than Tim every mth.
Each of them spends \$2000 and saves the rest every month.
When Fred has saved \$2600, Tim only saved \$1700.

a) how long does it take Tim to save \$1700?

b) how much does Tim earn in a month?

Step 1: Since both Fred and Tim spent the same amount of money, we draw 2 boxes to represent the \$2000 each of them spent.

Step 2: As Fred saved \$90 more than Tim every month, we draw a longer box for Fred and a shorter one for Tim to represent the amount of money saved each month.

Step 3: The above model represents the total spending and savings for the 1st month for both of them. Since this pattern will be repeated month after month, we draw a dotted line to represent the repetition of this behaviour.

(a)

Difference in Total Savings = \$2600 - \$1700 = \$900

Difference in Monthly Savings = \$90

Number of months taken to accumulate the total difference in savings = \$900 / \$90 = 10 months

Thus, Tim took 10 months to save \$1700.

(b)

Since Tim saved \$1700 in 10 months

His savings per month = \$1700 / 10 months = \$170 per month

Thus, his salary = \$2000 + \$170 = \$2170 per month.