Question

Ankit going to his school at 30 kmph speed and comes back to his house at 40 kmph. In all he has taken 70 mins. find the distance between his house and the school?

Answer 1

hi friend,
total speed= 70km/h=19.4 m/s
total time   = 70 minutes = 4200 seconds
total distance = 2X distance between his home and school.
total distance= 4200X 19.4 =81,480 m
but distance from his home = 81480/2=40,740metres or 40.74 kms
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Answer 2

method 1 :-

A ======================B
let A is Ankit's house and B is school
distance between A and B is D km
we know,
Time = distance/speed
when Ankit goes to school with speed 30km/h time taken by him T1 (let)
T1 = D/30 hours

again Ankit goes to house from school
with speed 40km/h take Time T2( let )
T2 = D/40 hours

according to question ,
T1 + T2 = 70 minutes = 70/60 hrs
D/30 + D/40 = 7/6
D{ 7/120} = 7/6
7D/120 = 7/6
D = 20 km
hence distance between school and house is 20 km

method 2 :-
=================
average speed of Ankit =2V1V2/(V1+V2)
where V1 and V2 are Ankit's speed from house to school and school to house .

now,
here V1 = 30 km/h
V2 = 40 km/h
average speed = 2×30×40/(30+40) =120/7 km/h
time taken = 70/60 hr =7/6 hr
now,
distance = speed × time
=120/7 × 70/60
=20 km