By how much per cent must a motorist increase his speed in order to reduce by 20%, the time taken to cover a certain distance?

• since distance is fixed, so time and speed have inverse relationship,,i.e, T1/T2= S2/S1
  now let by x% speed increases,
  then S2= S[(100+x)/100]
  and T2= T1*(1-20/100)= 4/5 * T1 (given time is reduced by 20 %)
  
  now T1/T2= S2/S1
  
  T1/(4/5*T1)= (100+x)/100* S1/S1= > 100+x= 125 => x=25%
  hence speed increases by 25 %.
• 9 years agoHelpfull: Yes(5) No(0)
• here distance is unchanged.
  so T2=4/5*T1 i.e T1/T2=5/4=S2/S1 AS T1/T2=S2/S1
  HERE WE NEED TO FIND S2 %.
  S2=5/4*S1
  S2%=5/4*100*S1%
  =125 S1%.
  SO INCREASED SPEED % IS 125-100= 25%
• 9 years agoHelpfull: Yes(0) No(0)