Answer:
To calculate the percentage change when a price of £40 is increased to £70, we can use the following formula:
Percentage Change = (New Value - Old Value) / Old Value * 100
Plugging in the numbers:
Percentage Change = (£70 - £40) / £40 * 100 = £30 / £40 * 100 = 75%
So the price has increased by 75%.