Question

How do you know that the product 221×331 is rational?

Answer 1

221 is rational since 221 = 221/1

So is 331 because 331 = 331/1

The product of any two rational numbers is also rational

--------------------------

Proof:

Let x = p/q and y = r/s be two rational numbers. The q and s values are nonzero.

Their product is

x*y = (p/q)*(r/s)

x*y = (p*q)/(r*s)

which is a ratio of two integers pq and rs, so (p*q)/(r*s) is rational