Researchers carry out a usability test of a machine used to pay for car parking. 5 participants take part in the test. The following list summarises the consequences of 4 usability problems found in the test. Rank order the problems from most severe to least severe.
1 This problem caused 3 participants to backtrack and re-start the transaction.
2 This problem caused 1 participant to pay for a longer parking period than was necessary.
3 This problem caused 5 participants to notice a typing error in the instructions.
4 This problem caused 4 participants to underpay for parking.