Share

If the Speed of a Car is Increased by 10 Km per Hr, It Takes 18 Minutes Less to Cover a Distance of 36 Km. Find the Speed of the Car. - ICSE Class 10 - Mathematics

Question

If the speed of a car is increased by 10 km per hr, it takes 18 minutes less to cover a distance of 36 km. Find the speed of the car.

Solution

Let the speed of the car be x km/hr.

Distance = 36 km

Time taken to cover a distance of 36 km = 36/x hrs

(Time = Distance/Speed)

New speed of the car = (x + 10) km/hr

New time taken by the car to cover a distance of 36 km = 36/(x + 10) hrs

From the given information, we have:

36/x - 36/(x + 10) = 18/60

(36x + 360 - 36x)/(x(x + 10)) = 3/10

360/(x^2 + 10x) = 3/10

120/(x^2 + 10x) = 1/10

x^2 + 10x - 1200 = 0

(x + 40)(x - 30) = 0

x = -40,30

But speed cannot be negative So x = 30

Hence the original speed of the car is 30 km/hr

Is there an error in this question or solution?

APPEARS IN

Selina Solution for Selina ICSE Concise Mathematics for Class 10 (2018-2019) (2017 to Current)
Chapter 6: Solving (simple) Problems (Based on Quadratic Equations)
Ex.6C | Q: 2

Video TutorialsVIEW ALL 

Solution If the Speed of a Car is Increased by 10 Km per Hr, It Takes 18 Minutes Less to Cover a Distance of 36 Km. Find the Speed of the Car. Concept: Quadratic Equations.
S