A road atlas gives these distances. Route A: Delhi to Agra 233 km, then Agra to Kanpur 285 km. Route B: Delhi to Aligarh 130 km, then Aligarh to Kanpur 355 km. Which route is shorter, and by how much?

Add each route right through: Route A is 233 + 285 = 518 km and Route B is 130 + 355 = 485 km, so Route B is shorter by 518 − 485 = 33 km. Comparing only the first legs, 233 against 130, suggests a saving of 103 km; comparing only the second legs, 285 against 355, suggests Route A saves 70 km. The two halves point in opposite directions, which is exactly why only the totals settle the question.