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?
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.
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.
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.