It took Malcom 3.5 hours to drive from city A to city B. On his way back to city A, he increased his speed by 20 km per hour and it took him 3 hours.
Find the average speed for the whole journey. Options:	A) 134.9 km/hr	B) 129.2 km/hr	C) 119.6 km/hr	D) 140.5 km/hr	E) 155.3 km/hr
Let x and x + 20 be the speeds of the car from A to B and then from B to A. Hence the distance from A to B may expressed as 3.5 x and the distance from B to A as 3(x + 20)   The average speed = total distance / total time = (3.5 x + 3 (x + 20)) / (3.5 + 3)   The distance from A to B is equal to the distance from B to A, hence: 3.5 x = 3(x + 20). Solve for x to obtain x = 120 km/hr.   We now substitute x by 120 in the formula for the average speed to obtain.   average speed = 129.2 km/hr   correct answer 129.2 km/hr)129.2 km/hr
<result>B</result>
It took Malcom 3.5 hours to drive from city A to city B. On his way back to city A, he increased his speed by 20 km per hour and it took him 3 hours.
Find the average speed for the whole journey.