Question

What is 9 plus 10???​

Answer 1

Answer:

21

Here’s legitimate proof that 9+10=21

(9 + 10) (base x) = 21 (base y)

9(1) + [1(x) + 0(1)] = 2(y) + 1

Simplify and solve for y:

2y = 8 + x

y = 4 + x/2

Since we have number bases, we want x and y to be positive integers. The term x/2 requires that x be a positive even number.

Also since 9 is in base x, we have x ≥ 10, as the digit 9 would not be used for a base 9 or smaller.

Thus we have the pairs of solutions:

x = 10, so y = 9

x = 12, so y = 10

x = 14, so y = 12

…

x, y = 4 + x/2 … Therefore 9+10=21!