Solving systems by elimination

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step-by-step explanation:

in counting the number of heads in 4 coin flips, the probability that we get exactly one head is the probability that we get anyone of the following 4 outcomes: httt, thtt, ttht, or ttth. each has probability 1/16, so the probability to get exactly one head in 4 flips is 1/16 + 1/16 + 1/16 + 1/16 = 4/16 = 1/4.

well it says right there your brother is 13; "your age". so lets keep it simple. you are 13 years old and there is no way to put this into any kind of equation without wanting to tear your hair out. who came up with this?