Question 650788
  <pre><font face = "Tohoma" size = 3 color = "indigo"><b> 
Hi,
old combine, crop can be harvested in 60 hours,
new combine can do the same job in 20 hours.
How many hours{{{highlight(x)}}} would it take to harvest the crop with both combines operating?
PER hour KEY
 1/60 + 1/20 = 1/x  |Multiplying thru by 60x so as all denominators = 1
  x  + 3x = 60
     4x = 60
      x = 15hrs it would take with both combines operating