# Video: KS2-M16S • Paper 2 • Question 8

Maria bakes cakes and sells them in bags. She uses this formula to work out how much to charge for one bag of cakes. Cost = number of cakes × 20p + 15p for the bag. How much will a bag of 12 cakes cost in pounds? Olivia buys a bag of cakes for £5.15. Use the formula to calculate how many cakes are in the bag.

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### Video Transcript

Maria bakes cakes and sells them in bags. She uses this formula to work out how much to charge for one bag of cakes. The cost equals the number of cakes multiplied by 20 pence plus 15 pence for the bag. How much will a bag of 12 cakes cost in pounds? Olivia buys a bag of cakes for five pounds and 15 pence. Use the formula to calculate how many cakes are in the bag.

This question has two parts. The first part asks us to calculate how much a bag of 12 cakes will cost in pounds. We know the number of cakes is 12. We need to multiply this by 20 pence. 12 times 20 pence equals 240 pence. Then we need to add 15 pence for the cost of the bag. 240 pence plus 15 pence is 255 pence. We’re asked to write the answer in pounds. We write 255 pence as two pounds 55.

In the second part of the question, we’re told how much money Olivia has spent: five pounds and 15 pence. We’re asked to use the formula to calculate how many cakes are in the bag. We know that a bag costs 15 pence. So we could subtract this from the five pounds 15 and that will tell us how much money Maria spent on cakes. Five pounds 15 take away the 15 pence leaves us with five pounds to spend on cakes.

We know that the cost is calculated by multiplying the number of cakes by 20 pence. So to find out how many cakes Maria bought with her five pounds, we need to divide five pounds by 20 pence. We know that five 20ps make one pound. So 25 20ps must make five pounds because 25 is five times greater than five. There are 25 cakes in the bag.