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CBSE Class 10 Answered

A passenger train takes 3 hours less for a journey of 360 km if it's speed is increased by 10 km/hr from its usual speed. Find the usual speed?
Asked by ujjwal.udgamer | 07 Feb, 2020, 01:18: PM
answered-by-expert Expert Answer
 
Let the usual speed of a train = x km/hr
 
According to the condition, we get
 
T2 - T1 = 3        .... (Time = Distance/Speed)
begin mathsize 16px style 360 over straight x minus space fraction numerator 360 over denominator straight x plus 10 end fraction equals 3
rightwards double arrow 360 open parentheses 1 over straight x minus fraction numerator 1 over denominator straight x plus 10 end fraction close parentheses space equals 3
rightwards double arrow fraction numerator straight x plus 10 minus straight x over denominator straight x squared space plus space 10 straight x end fraction space equals 1 over 120
rightwards double arrow straight x squared space plus space 10 straight x space minus space 1200 space equals space 0
rightwards double arrow straight x squared space plus 40 straight x space minus 30 straight x minus space 1200 space equals space 0
rightwards double arrow straight x open parentheses straight x plus 40 close parentheses minus 30 left parenthesis straight x space plus space 40 right parenthesis space equals space 0
rightwards double arrow open parentheses straight x plus 40 close parentheses open parentheses straight x minus 30 close parentheses space equals space 0
rightwards double arrow straight x space equals space minus 40 space or space straight x space equals space 30
Speed space can apostrophe straight t space be space negative.
Therefore space the space ususal space speed space of space straight a space train space is space 30 space km divided by hr. end style
Answered by Yasmeen Khan | 07 Feb, 2020, 02:33: PM
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