Can someone me on my last problem? #10

Ok but what did i do wrong and if you never studied the subject how did you know i was wrong

Based on my small expertise in this subject,

the answer should be 1/(20)^22

the logic is the same as a coin flip
1st flip: call for heads, 1/2 chance
2nd: call for heads, (multiply by self) 1/2 x 1/2= 1/4 chance
3rd: heads, 1/4 x 1/2= 1/8
and so on...

I'm gonna have to say about 13 percent