You drive on interstate 10 from san antonio to houston, half the time at 54 km/h and the other half at 118 km/h. on the way back you travel half the distance at 54 km/h and the other half at 118 km/h. what is your average speed?

Explanation:

As we move from San Antonio to Houston

let the distance is "d" from Antonio to Houston

Half the time it moves with 54 km/h and next half the time it moves 118 km/h

so we will have

so total time is

now while his return journey half the distance he move with 54 km/h and next half distance with speed 118 km/h

so we have time of return journey

so now we have

now for the average speed we know that