chandeep01
Nicole cycles at a constant rate of 20 kilometers per hour, and is passed by Jessica, who cycles at a constant rate of 30 kilometers per hour. If Jessica cycles at her constant rate for x minutes after passing Nicole, then stops to wait for her, how many minutes will Jessica have to wait for Nicole to catch up to her?
a) x minutes
b) x/2 minutes
c) 2x/3 minutes
d) 3x/2 minutes
e) 2x minutes
We can classify this problem as a “catch-up” rate problem, for which we use the fact that distance travelled by Nicole = distance travelled by Jessica.
We are given that Nicole cycles at a constant rate of 20 kilometers per hour and is passed by Jessica, who cycles at a constant rate of 30 kilometers per hour. We are also given that Jessica cycles at her constant rate for x minutes after passing Nicole, and then stops to wait for her. We can let t be the waiting time in minutes; that is, Nicole has to cycle x + t minutes to catch up to Jessica, who has to cycle x minutes only.
Since distance = rate x time, we can calculate each person’s distance in terms of t and x. However, the rate is in km per
hour, but the time is in
minutes. Thus we need to convert the time from minutes to hours. Recall that there are 60 minutes in an hour. Thus, x minutes = x/60 hours and x + t minutes = (x + t)/60 hours.
Nicole’s distance = 20[(x + t)/60] = (x + t)/3
Jessica’s distance = 30(x/60) = x/2
We can equate the two distances and determine t in terms of x.
(x + t)/3 = x/2
2(x + t) = 3x
2x + 2t = 3x
2t = x
t = x/2
Answer: B