Expenditure:

Total expenditure of three passengers =90*3=270 yuan.

Income:

The shopkeeper gets 250 yuan, and the clerk gets 20 yuan.

Expenditure = income, no problem.

Wrong algorithm:

Confuse the concepts of expenditure and income.

Add part of the expenditure and income together, and the expenditure of 270 yuan and part of the income of 20 yuan =290 yuan. The results showed nothing and made no sense.

Just like this, for example, the tourists spent 270 yuan and the shopkeeper took 250 yuan, which adds up to 520 yuan. Compared with 300 yuan, where did 220 yuan come from?

No one is wrong, but the brain of the 250 shopkeeper who asked the question of 270+20=290 is short-circuited.