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28. A car covers a distance of 840 km at a constant speed.If the speed of the car would have been 10 km/h less,then it would have taken 2 hours more to cover thesame distance. What is the actual speed of the car?यदि एक कार की चाल 10 किमी/घण्टे कम होती तो 840किमी की दूरी तय करने में 2 घण्टे अधिक लगते, कार कीवास्तविक चाल ज्ञात कीजिए-(a) 60 kmph( (b) 70 kmph(c) 80 kmph( (d) 90 kmph |
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Answer» Answer: LET the ORIGINAL speed be x km/hr. Then, [ 840/x - 840/( x + 10) ] = 2 ⇒ 840 (x + 10) - 840x = 2x (x+10) ⇒ x2 + 10X - 4200 = 0 ⇒ (x + 70) (x - 60 ) = 0 ∴ x = 60 km/hr. |
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