Ex 4.3 Q8. NCERT Solution to Class 10 Exercise

Video Explanation

Step 1: Frame equations based on the information about speed of train.
Let the speed of the train be s km/hr.
Time taken to cover a distance of 360 km at s km/hr = $$frac{360}{s}$ hr If the speed of the train had been 5 km/hr more, speed of train would be$s + 5) km/hr.
Time taken to cover 360 km @ (s + 5) km/hr = $$frac{360}{s + 5}$ hr Time taken to cover 360 km at$s + 5) km/hr is 1 hr lesser than time taken at s km/hr
i.e., $$frac{360}{s + 5}$ = $\frac{360}{s}$ - 1 $\frac{360}{s + 5}$ - $\frac{360}{s}$ = -1 Because s ≠ 0 and s ≠ -5, multiply the equation by$s + 5)s
360(s) - 360(s + 5) = -s (s + 5)
360s – 360s - 1800 = -s2 – 5s
s2 + 5s - 1800 = 0

Step 2: Factorize the quadratic equation to find s

s2 + 45s – 40s – 1800 = 0
s(s + 45) – 40(s + 45) = 0
(s + 45) (s – 40) = 0
s = -45 or s = 40
Speed cannot be negative ∴ s = 40 km/hr