Two numbers have a product of 80 their sum is 21?

Let the two numbers be x and y.

According to question, x * y = 80.....................(1)

and x + y = 21.................................................(2)

(1) implies that y=80/x......................................(3)

Now, Substituting this value in equation (2) we get,

x + 80/x=21

or x2 - 21x + 80=0.

Solving this quadratic equation x=16 and x=5.

If x=16, then (3) implies y=5

If x=5, then (3) implies y=16.

Hence the two numbers are 16 and 5.