A shop's second counter takes 50% more money in a day than its first counter. The gap between the two counters' takings is what per cent of the second counter's takings?

Take the first counter as 100, so the second takes 150 and the gap is 50. The question asks for the gap against the SECOND counter: 50/150 = 1/3 = 33 1/3%. 50% is the same gap measured on the first counter - that is where the '50% more' came from in the first place, so quoting it back is the trap here. 66 2/3% is the first counter's takings as a share of the second's, and 150% is the second's as a share of the first's; neither of those is the gap.