Jules buys a washing machine. 20% VAT is added to the price of the washing machine. Jules then has to pay a total of £600 What is the price of the washing machine with no VAT added?

Remember that we have two values here, the price of the washing machine BEFORE and the price AFTER the 20% VAT increase. The value AFTER the increase is 600. To get to the value before, you can't simply subtract 20% of 600, because 20% of the ORIGINAL value was what the washing machine was increased by, not 20% of 600.
What we can see however is when you increase something by 20%, you can also think of it as multiplying something by 1.2. So you can simply divide 600 by 1.2 to get the original price. So 600/1.2 = 500, final answer.