In a sale a clothes shop reduces its price by 40%.a shirt usually costs £20 how much is it in sale

Do 10% first, and then times it by four, so 10% is £2 times 4 is £8, take it away from £20 is £12. Hope it helps

I've made a table which may help to explain.
   in %|£ percentage| Pounds
   100 | 20                               Given that 100% of the original price is 20 pounds
     10 | 2                                  You should be able to subtract £8 from the £20
    40 | 8
                     Finally giving you £12 for the shirt during the sale.

Documentation and time management