A train travels a distance of 480 km at a uniform speed. If the speed had been 8 km/hr. less, then it would have been taken 3 hours more to cover the same distance. Find the usual speed of the train. एक रेलगाड़ी एक 480 किमी. की दूरी को एक समान चाल से तय करती है | यदि चाल को 8 किमी./घंटा कम कर दी जाय, तो यह उसी दूरी को तय करने में 3 घंटे अधिक लेती है | रेलगाड़ी की मूल चाल ज्ञात कीजिये |

Let usual speed = x km/hr. Time at usual speed = 480/x hours. At reduced speed (x-8) km/hr, time = 480/(x-8) hours. Given: 480/(x-8) - 480/x = 3. Solving: 480x - 480(x-8) = 3x(x-8). 480x - 480x + 3840 = 3x² - 24x. 3x² - 24x - 3840 = 0. Dividing by 3: x² - 8x - 1280 = 0. Using quadratic formula: x = [8 ± √(64 + 5120)]/2 = [8 ± √5184]/2 = [8 ± 72]/2. x = 40 or x = -32 (reject negative). Speed = 40 km/hr. This matches option C.