Question

. A car travels 35 km in the first 30 minutes,
25 km in the next 20 minutes and 10 km
on the last leg of its journey. If the average
speed of the car is 70 km/h, find out how
long it takes to cover the last leg of its
journey.
[Ans.: 10 min​

Answer 1

Answer:

10 minutes

Explanation:

As per the provided information in the given question, we have :

• A car travels 35 km in the first 30 minutes,
• 25 km in the next 20 minutes and 10 km
• on the last leg of its journey.
• Average speed is 70 km/h.

We are asked to calculate the time taken to cover the last leg of its journey.

Let us assume the the time taken to cover the last leg of its journey as x minutes.

As we know that,

$\longmapsto \rm { Speed_{(avg)} = \dfrac{Total \; distance}{Total \; time} }$

According to the question,

$\longmapsto \rm { \dfrac{70 \; km}{1 \; h}= \dfrac{(35+25+10)\; km}{(30 + 20+ x) \; min} }$

• 1 hour = 60 minutes

$\longmapsto \rm { \dfrac{70 \; km}{60 \; min}= \dfrac{(35+25+10)\; km}{(30 + 20+ x) \; min} }$

Rearranging the terms.

$\longmapsto \rm { \dfrac{70 }{60 }= \dfrac{35+25+10 }{30 + 20+ x} }$

Performing addition.

$\longmapsto \rm { \dfrac{7 }{6 }= \dfrac{70 }{50+ x} }$

Now, we have to cross multiply the values in order to find the value of x.

$\longmapsto \rm { 6(70) = 7(50+ x) }$

Performing multiplication as we do in ordinary multiplication.

$\longmapsto \rm { 420 = 350 + 7x}$

Transposing 350 from R.H.S to L.H.S.

$\longmapsto \rm { 420 - 350 = 7x}$

Performing subtraction in L.H.S.

$\longmapsto \rm { 70 = 7x}$

Transposing 7 from R.H.S to L.H.S.

$\longmapsto \rm {\cancel{\dfrac{ 70}{7}} = x}$

Dividing 70 by 7.

$\longmapsto \bf{ 10 \; min = x}$

∴ It takes 10 minutes to cover the last leg of its to cover the last leg of its journey.

Answer 2

Answer:

Please see the photo for answere.