Question

a car covers 1/3 part of total distance with speed of 12 km/h , then second 1/3 part of total distance with speed 18 km/h and last 1/3 part of the total distance with speed 24 km/h . The average speed of car is​ ___
please answer fast

Answer 1

Answer
S
total
​
=S
1
​
+S
2
​
+S
3
​

S
1
​
=
3
S
​
V
1
​
=10kmh
−
1

S
2
​
=
3
S
​
V
2
​
=20kmh
−
1

S
3
​
=
3
S
​
V
3
​
=60kmh
−
1

∴t
1
​
=
V
1
​

S
1
​

​
=
3
S
​
×
10
1
​
=
30
S
​
h

t
2
​
=
V
2
​

S
2
​

​
=
3
S
​
×
20
1
​
=
60
S
​
h

t
3
​
=
V
3
​

S
3
​

​
=
3
S
​
×
60
1
​
=
180
S
​
h

∴V
any
​
=
total time taken
total distance
​


=
30
S
​
+
30
S
​
+
30
S
​

s
​
=
180
6S+3S+S
​

S
​


=
10S
180S
​


Ans) 18km/ph

Answer 2

Answer:

A car covers 1/3 part of total distance with speed of 20 km/hr & remaining distance with a speed of 44 km/hr. What is the average speed of the car?

Simplify your search for the most efficient HR Software .

Eric Ressner

Answered 2 years ago

Three answers posted so far. All solve the problem completely algebraically, and gratifyingly get the same answer. The approach is rigorously analytical and flawless.

I’m posting another answer with an easier way.

You’ll notice that the problem doesn’t tell us what the total distance is. One reasonable inference we can make is that … it doesn’t matter. So let’s make up a number that easy to work with. Say, 100 km.

First part of trip is 33.3 km x 1 hr20 km = 1.6665 hr

Second part of trip is 66.7 km x 1 hr44 km = 1.5159 hr

So the whole trip was 100 km3.1824 hr = 31.42 km/hr

Take-home: when the problem seems to require a number that isn’t given, you are seeing a way to solve it if only you had that number. The fact that you don’t have that number means the number isn’t needed to solve the problem, so you can just make one up. So make one up.

(That’s assuming it isn’t a multiple choice question where one of the answers is “Not enough information.” In that case, you’d have to get more analytic. As the previous answerers did.)

Step-by-step explanation: