Scaling revenue from a steady rate

Some questions give sales as a steady rate for one time period, such as units per day or per week, but ask for revenue over a different period. Work out the revenue for the period the rate is given for first, then scale it to the period you need by multiplying or dividing.

How to do it

1. Multiply the selling price by the number of units sold in the period the rate is given for.
2. Multiply or divide that revenue by the number of periods you are converting between. Multiply when scaling up to a longer period and divide when scaling down to a shorter period.

A market stall sells 15 jars of honey a day at £4.50 each. Daily revenue = 15 × £4.50 = £67.50. The stall trades 5 days a week, so weekly revenue = £67.50 × 5 = £337.50. Over a 4-week month, revenue = £337.50 × 4 = £1,350.

Going the other way, if the stall takes £1,350 over 20 trading days (4 weeks × 5 days), daily revenue = £1,350 ÷ 20 = £67.50.

Why work it out in stages

Finding the revenue for the period the rate is given for first keeps every figure tied to a time period you can check, so the amount you then multiply or divide is clearly a "per day" or "per week" amount. It also makes your working easy to follow, so a marker can see each stage and award method marks.

You can instead multiply the price by the total number of units for the whole period, but only once that total has actually been calculated, or when the question hands it to you. Assuming a total quantity that nobody has worked out is where answers go wrong, such as treating a daily sales figure as though it were already the figure for the whole month.