Question 1:
The given formula is

To make T, the subject we multiply both sides by 100:

This becomes

Divide both sides by PR

b) Amanda's principal is , P=€2565
The interest rate is 3.5% p.a. that is R=3.5
We want to find how many years, her money will gain an interest of I=€718.20
We substitute into the formula for T,

This simplifies to:
T=8
Therefore it will take 8 years
2) Percentage profit

The cost price of the 80 articles €200
The selling price is 3.5×80=€280
The profit =€280-€200=€80
The percentage profit is now



The percentage profit is 40%
Question 3)
Let the original price of the calculator be x.
Then 85% of this price will be:

This is the same as€32.89
We equate and solve for x.




The original price is €38.69