Question

A car takes $2$hr to reach a destination by travelling at the speed of $120$km/hr. how long will it take when the car travels at the speed of $80$ km/hr?

Answer 1

Hint:As it is given a car takes a certain amount of time to reach a destination with a certain speed in order to find the time firstly we will calculate the distance travelled by the car then after that we can find the time taken by the car with new speed

Complete step-by-step answer:
We are given speed of car is $60$km/hr and time taken by car is $2$hr to reach the destination to find the time taken to reach destination if speed is $80$km/hr
Let the time taken by car is $y$hours
Firstly we find the distance covered by car
Distance=speed × time
Substituting the values in formula
 $ = 60 \times 2$
$ = 120$km
As the speed of the car increases the time decreases because the distance remains same
Let us consider a table:

Speed of car	60	80
Time taken by car	2	y

They are in inverse proportion
Using the ${x_1}{y_1} = {x_2}{y_2}$
$60 \times 2 = 80 \times y$
Divide it by $80$
$\dfrac{{60 \times 2}}{{80}} = y$
We will get,
$\dfrac{3}{2} = y$
Converting unlike fractions into mixed fractions
$y = 1\dfrac{1}{2}$hours
Hence, car will take $1\dfrac{1}{2}$ hours to reach the destination

Note:The speed of a moving body is the distance travelled by it in unit time if the distance is in km and time is in hr then the speed is km/hr we can also find the time here by applying the formula of time
$\text{Time}= \dfrac{\text{Distance}}{Speed}$
Time=$\dfrac{{60 \times 2}}{{80}}$ $ = \dfrac{3}{2}$hours
Time=$1\dfrac{1}{2}$hours
Students mainly do mistakes in calculation or applying formula