A boy started for a school which is 12 km from his home by bicycle at a speed of 8 km/hr but after 1

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28 Sep 2022 Time Distance & Speed

A boy started for a school which is 12 km from his home by bicycle at a speed of 8 km/hr but after 15 minutes he remembers that he forgot one of the book at home, so he increases his speed and returns back to home and also reaches to school in time. The percentage increase in his speed is

OPtion

1) 33.33%
2) 20%
3) 15%
4) 30%
5) 12.5%
6) 37.5%
7) 40%
8) 25%
9) 66.55%
10) None of these

Solution

Usual time to reach school=12/8=1.5 hrs
Distance covered in 15 min. at a speed of 8 km/hr=(15/60)*8=2 km
So, he comes back 2 km to home and again return to school at a speed of say 'x' km/hr.
Then, usual time of 1.5 hrs = 15 min. + Time taken for the journey of (2+12) km with increased speed.
1.5 = (1/4) + (14/x)
x=11.2
Therefore % increase in the speed = [(11.2 - 8)/8]*100 = 40%
Correct Option 7)

Correct Option: 7 Best Solution (4)

G.S.Kantharao   1 year AGO

Regular time to be taken =12/8
After 15 m he traveled 2km
So real distance to travel is =12+2=14km
Real time taken
=14/s=(12/8 - 1/4)=14/s=10/8
S=11.2kmph
%of increase=(11.2-8)100/8=40%
My option is 7 👈

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AAKASH RAWAT   1 year AGO

Boy to school distance 12 km
Speed of bicycle 8 km/ hr
Time taken to go to school = 12/8 = 3/2hr
After 15 minutes ,
d = (15/60) ×8 = 2km
Now he will travel 14km to reach to school
Time left to reach school = (3/2) - 15/60 = 5/4 hr
Now speed will be 14/(5/4) = 56/5 km/ hr
percentage change in speed = (56/5)/8 ×100 = 140%
Increase in speed( 140 - 100)% intial speed 100%
= 40%

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RAMADURAI NATESAN   1 year AGO

Initial time to reach school = 90 minutes.
Distance travelled in 75 m =14 km.Speed = 60*14/75 = 11.20km
% increase = 40

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Dr.Dipin Singh   1 year AGO

Boy will take 1.5 hrs to cover 12 kms at speed of 8 km/hr.
In 15 minutes, he covered 2 kms.
Now to reach school in time, he should cover 14 kms in 1.25 hrs or 5/4 hrs.
So new speed =14*4/5=56/5 kmph which is 7/5 or 1.4 times of earlier speed.
So increase in speed=40%

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