A £380 item rises 20%, then a further 10% on the new price. What is the final price?

Successive percentages multiply: apply each factor in turn (e.g. ×1.10 then ×1.20). They never simply add. The correct answer is £501.60. Traps to avoid: £410.00 comes from the "added raw" error; £494.00 comes from the "additive percents" error; £456.00 comes from the "one step only" error; £418.00 comes from the "other step only" error.