ScottTargetTestPrep
nalinnair
A certain bridge is 4,024 feet long. Approximately how many minutes does it take to cross this bridge at a constant speed of 20 miles per hour? (1 mile = 5,280 feet)
(A) 1
(B) 2
(C) 4
(D) 6
(E) 7
The length of the bridge, in miles, is:
4,024/5,280 = 503/660, which is about 500/660 = 50/66 = 25/33.
Using the formula: time = distance/rate, we see that the time, in hours, is:
[25/33]/20 = 25/(33 x 20) hours
So the time in minutes is:
25/(33 x 20) x 60 = (25 x 3)/33 = 25/11, which is about 2 minutes.
Answer: B
ScottTargetTestPrepI decided to convert the rate...
I did (20 miles/1 hr)*(5280 ft/1 mile) --> 105,600 feet/1hr
I then set this up in my rt=d
(105,600 ft/1 hr)*(t)=4,024 ft
I then solved and approximated so the time = 4,024/105,600 --> 4,000/100,000 = 4/100
Then I converted to minutes (4/100)*60 = 2.4, and since i was dividing by ~105,000 before simplifying, the answer is even smaller than 2.4 --> 2 makes the most sense.
With this approach, I would be so appreciative to learn if you think that my work correct/efficient