In a race from pt. X to pt Y and back, Jack averages 30miles/hr to pt Y and 10 miles/hr back
to pr X.Sandy averages 20 miles/hr in both directions. If Jack and Sandy start race at same tym,
who’ll finish 1st

• The Average speed of Jack is 15mph by 2xy/x+y.
  and sandy is 20miles/hr...
  by comparing both speed sandy will reach first..
• 11 years agoHelpfull: Yes(40) No(3)
• jack's average speed will be (30+10)/2=20 miles/hr
  since he covered same distance both times
  so, both will reach same time at the finish
• 11 years agoHelpfull: Yes(0) No(27)
• at same time since distance and time is same
  avg=s1+s2/2
  
• 7 years agoHelpfull: Yes(0) No(0)
• let D=60Km
  jack avg time= 60/30+60/10=2+6=8
  sandy avg time=60/20+60+20=3+3=6
  thus, sandy will finish first.
• 7 years agoHelpfull: Yes(0) No(0)
• 3 answers · Geography
  Best Answer
  They will tie. 30 one way and 10 the other is an average of 20, same as Sandy.
  trea0766 · 1 decade ago
  Comment 1 5
  Answers
  To solve this we can just make a "guess" which will make this a little simpler...we can just "guess" that the distance is 1 mile from X to Y...this way we will be working with easier numbers.
  First Jack
  X->Y
  If the distance is 1 mile and Jack can run for 30 miles in 1 hour we can see that it would take jack 2 minutes to get there [1 mile*(1 hour/30 miles)*(60 minutes/1hour)] = 2 minutes.
  Y->X
  If he can run 10 mph on the way back then it would be [1 mile*(1 hour/10 miles)*(60 minutes/1hour)] = 6 minutes.
  The total time taken it is 8 minutes.
  
  Sandy
  If she can run 20 mph on the way back then it would be [1 mile*(1 hour/20 miles)*(60 minutes/1hour)] = 3 minutes.
  and she does that twice so it takes her 6 minutes.
  
  It takes Jack 8 minutes and it takes Sandy 6 minutes...so Sandy finishes first.
• 5 years agoHelpfull: Yes(0) No(0)