My book asked \"what are the chances of flipping a coin 4 times and getting \"He

Question

My book asked "what are the chances of flipping a coin 4 times and getting "Heads" at least twice. I answered it by saying that the chance of getting "Heads" only once is X, and the chance of getting it at least twice is (1 - X). I then used the binomial formula to determine the chance of getting it only once:

4C1 * 0.5^1 * 0.5^3

This comes out to be 0.25, so the chance of getting Heads at least twice must be 0.75

Yet this answer is not correct, because my book says the chance is 11/16

What am I doing wrong?
Thank you

Explanation / Answer

this is bionomial dsitribution.

no of events n = 4   probability of success = p of getting head = 1/2

now

atleast twice heads menas = 2 heands or 3 heads or 4 heads

this

P(X=2)+P(X=3)+P(X=4) = 4C2 * 0.5^1 * 0.5^3 + 4C3 * 0.5^1 * 0.5^3 + 4C4 * 0.5^1 * 0.5^3

SIMPLYFYING

4C2 + 4C3 + 4C4 / 16 = 6+4+1 / 16    = 11/16

thus ans.

Related Questions

Navigate

• Browse (All)
• Browse M
• Subjects

---

---

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.