Question

What is the probability to have exactly prime number of heads when a coin is tossed 5 times? 1] 9/32 2] 13/32 3] 21/32 4] 1?

Answer 1

HHHHH;THHHH, HTHHH, HHTHH, HHHTH, HHHHT;TTHHH, THTHH, THHTH, THHHT, HTTHH, HTHTH, HTHHT, HHTTH, HHTHT, HHHTT;TTTHH, TTHTH, TTHHT, THTTH, THHTT, THTHT, HTTTH, HTTHT, HTHTT, HHTTT;TTTTH, TTTHT, TTHTT, THTTT, HTTTT;TTTTT. 

There are 32 possible outcomes.

P[of getting prime number of heads]=21/32