Question 195410
1] A distance is covered in 3 hours 48 min. at 5 kmph. how much time will be taken to cover it at 28.5 kmph ?
:
Convert 3 hr 48 min to hrs; 3 + 48/60 = 3.8 hrs
:
we can use inverted ratio here, (Time varies inversely to speed)
let t = time to cover the dist at 28.5 km/hr
{{{5/28.5}}} = {{{t/3.8}}}
Cross multiply
28.5t = 5*3.8
:
28.5t = 19
t = {{{19/28.5}}}
t = {{{2/3}}} hr to cover that dist at 28.5 km
;
Check solution by finding the dist at each speed and time
.67 * 28.5 ~ 19 km
3.8 * 5 = 19 km
:
:
2] Rita goes to school at 10 kmph & reaches the school 6 minutes late.
Next day, she covers this distance at 12 km/hr & reaches the school 9
minutes earlier than the scheduled time. 
What is the distance of her school from her house?
;
Let's just say the time difference between the two trips is 15 min, which {{{1/4}}}hr
Write a time equation Time = {{{dist/speed}}}
12 km time + {{{1/4}}}hr = 10 km time 
{{{d/12}}} + {{{1/4}}} = {{{d/10}}}
Multiply equation by 60 to get rid of the denominators, results:
5d + 15 = 6d
:
15 = 6d - 5d
d = 15 km is the distance
;
;
Check solution by finding the time of each trip
15/10 = 1.5 hr
15/12 = 1.25 hr
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differ= .25 hr which is 15 min