Last updated at Feb. 25, 2017 by Teachoo

Transcript

Ex 4.3 ,8 A train travels 360 km at a uniform speed. If the speed had been 5 km/h more, it would have taken 1 hour less for the same journey. Find the speed of the train. Let the speed of train be x km/hr From (1) (x + 5) (360/๐ฅ " โ 1" ) = 360 (x + 5) ((360 โ ๐ฅ)/๐ฅ) = 360 (x + 5) (360 โ x ) = 360x x(360 โ x) + 5(360 โ x ) = 360 x 360x โ x2 +5(360) โ 5x = 360 x 360x โ x2 + 1800 โ 5x = 360 x 360x โ x2 + 1800 โ 5x โ 360 x = 0 โ x2 โ 5x โ 360 x + 360x + 1800 = 0 โ x2 โ 5x + 1800 = 0 0 = x2 + 5x โ 1800 x2 + 5x โ 1800 = 0 We factorize by splitting the middle term method x2 + 45x โ 40x โ 1800 = 0 x (x + 45) โ 40 (x + 45) = 0 (x + 45) (x โ 40) = 0 Hence x = โ 45, x = 40 are the roots of the equation We know that Speed of train = x So, x cannot be negative โด x = 40 is the solution So, Speed of train = x = 40 km/hr

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