Question 84672
Let the time taken by Allen to plant a field of corn = x hrs

Then time taken by Eric = 2x hrs

Quantity planted by Allen in 1 hr = 1/x

Quantity planted by Eric in 1 hr = 1/2x

Quantity planted by both in 1 hr = 1/x + 1/2x

                                 = 3/2x

But given they work together and finish in 5 hrs

==>      3/2x = 1/5

==> 2x = 15 [multiplying both sides by LCD = 10x]

==> x = 15/2

 ==> x = 7 1/2 

Thus time taken by Allen to plant a field of corn = 7 1/2 hrs

time taken by Eric to plant a field of corn = 2x = 15 hrs