Question 256566
Katrina drove her car to Boston at a speed of 100 kph (kilometers per hour).
 She drove back at 75 kph. The total driving time was 7 hours.
 How far away was Boston?
:
Let d = distance to Boston
:
Write a time equation: Time = dist/speed
:
To B. time  +  from B. time = 7 hrs
{{{d/100}}} + {{{d/75}}} = 7
Multiply by 300 to get rid of the denominator, results
3d + 4d = 300(7)
7d = 2100
d = {{{2100/7}}}
d = 300 mi to B.
:
:
Check solution, find the time of each trip
300/100 = 3 hrs
300/75  = 4 hrs
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total  = 7 hrs
;
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That's pretty easy, right?