Bunuel wrote:

marcodonzelli wrote:

If a certain coin is flipped, the probability that the coin will land heads is 1/2. If the coin is flipped 5 times, what is the probability that it will land heads up on the first 3 flips and not on the last 2 flips?

A. 3/5

B. 1/2

C. 1/5

D. 1/8

E. 1/32

We want the probability that coin will land heads up

on the first 3 flips and not

on the last 2 flips. So there is

ONLY one favorable outcome, namely heads up

on the first 3 flips and tails up

on the last 2 flips: HHHTT.

# of total out comes is 2^5=32.

P=favorable/total=1/32.

Answer: E.

In this problem is the above the equivalent of some of these other answers (and how I approached the problem) of simply doing

Chance for tails & chance for heads both = 1/2

Chance of heads 1/2 * chance of heads *chance of heads 1/2 * chance of heads 1/2 * chance of tails 1/2 * chance of tails 1/2?

I see the above total as 2^5 over 1 possibility so the numbers are the same but for straight forward problems such as this one is the listed 1/2*1/2*1/2 an acceptable approach or just a coincidence it works for this problem?

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Please help me find my lost Kudo's bird