In a survey of 1,500 commuters, 46% use a bus, 34% use a two-wheeler and the rest walk. How many more commuters use a bus than walk?

Walkers make up 100 - 46 - 34 = 20% of the commuters, that is 300 people, and bus users are 46% of 1500 = 690. The gap is 690 - 300 = 390. 180 is 12% of 1500, the bus-to-two-wheeler gap - the wrong pair. 300 and 690 are the two groups themselves rather than the difference between them.