On a farm, the number of chickens was more than the number of ducks. After 20% of the chickens were sold, there were 800 less chickens than ducks on the farm. How many ducks were there on the farm? ___ducks

1 Answer
Jul 7, 2018

d=(4000+4x) where x is an integer greater than 0

Explanation:

c>d .......................................... (1)

d(c20100c)=800 ..............(2)

so from (2)
d0.8c=800

multiply through by 5 to get whole numbers

5d4c=4000

5d4000=4c

4c=5d4000

c=5d40004

c=5d440004

c=5d41000 .........................(3)

substitute for c in (1).

1.25d1000>d

1.25dd1000+1000>dd+1000

0.25d>1000

d>4000

but c must be a whole number so
in eqn (3) the term 5d4 must be a whole number,
so d must be divisible by 4.

Combining both of these conditions gives:

d=4000+4x where x is an integer greater than 0