An electric bus has onboard instruments that report the total electricity consumed since the start of the trip, as well ...

Question

An electric bus has onboard instruments that report the total electricity consumed since the start of the trip, as well as the total distance covered. During a single day of operation, the bus travels on stretches M, N, O, and P, in that order. The cumulative distances travelled and the corresponding electricity used (kWh) are shown in the table below.

Stretch | Cumulative distance (km) | Electricity used (kWh)
   M    |            20            |           12
   N    |            45            |           25
   O    |            75            |           45
   P    |           100            |           57

The stretch where the electricity consumption per km is minimum is:

A. M   B. N   C. O   D. P

Accepted Answer

Stretch P has the minimum electricity consumption per km at 0.48 kWh/km. The instruments record running totals, so the table gives cumulative data. To find per-stretch values we take differences between consecutive rows. Then we compute the electricity-per-km ratio for each individual stretch. The stretch with the lowest ratio is the most efficient and is the answer.