Question posted by Kelvin and Jeanie from Singapore:

Grade/Level: Primary 4

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?

Answer:

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.