I think this is $\frac{2+20}{2}=11$

The answer is 11.

Can someone say why?

RZSIANsw1Z wrote: Can someone say why? You can get $1$, $0$ times. You can get $2$, $1$ times. You can get $3$, $2$ times. You can get $4$, $3$ times. You can get $5$, $4$ times. You can get $6$, $5$ times. You can get $7$, $6$ times. You can get $8$, $7$ times. You can get $9$, $8$ times. You can get $10$, $9$ times. You can get $11$, $10$ times. You can get $12$, $9$ times. You can get $13$, $8$ times. You can get $14$, $7$ times. You can get $15$, $6$ times. You can get $16$, $5$ times. You can get $17$, $4$ times. You can get $18$, $3$ times. You can get $19$, $2$ times. You can get $10$, $1$ times.