What plus what gives you 21?

Answer 1

"what plus what gives 21" or simply we can say: x + y = 21.

Choose any value of x(say, 2) then we get y = 21-2 =19.

If we put x = 20 then we get y = 1.

We can write a few pairs satisfying the condition as: (1,20), (9,12), (-21,42), (0,21), (2,19),...

There exists infinitely many values of x and y.

However, if we talk about only natural numbers then we can write all the values of x and y. But, if we talk about real numbers then we have infinite values of x and y.