✔ 最佳答案
P(head at least twice)
= 1 - P(no head) - P(head only show once)
= 1 - (1/2)^5 - [(1/2)^5]*5
(1/2)^5 --> all 5 are tail, no head
(1/2)^5 * 5 --> only 1 head, others are tail, ie. HTTTT, THTTT, TTHTT, TTTHT & TTTTH
= 1 - 1/32 - 5/32
= 26/32
= 13/16