One hour after Yolanda started walking from X to Y, a distance of 45 miles, Bob started walking along the same road from Y to X. If Yolanda's walking rate was 3 miles per hour and Bob's was 4 miles per hour, how many miles had Bob walked when they met?
In one hour, Yolanda walked: 3*1 = 3 miles
Therefore, the distance when Yolanda and Bob started at the same time is: 45-3 = 42 miles
Since they are walking toward each other, find out how long it takes for both of them to meet by adding speed:
4+3 = 7mph
Therefore, it will take them: (1/7)*42 = 6 hours to meet
In 6 hours, Bob walked: 6*4 = 24