Question on conditional probability

Three coins are tossed simultaneously. Find the probability that all coins shows head given at least one of the coinw shows a head.

Will love to have answer which explain in the context of conditional probability.

Assuming that these coins are fair,
A be the event of getting atleast 1 heads.
B be the event of getting all 3 heads.
We need to find P(B|A).
P(A) = 1/2 + 1/4 + 1/8 = 7/8
P(B) = 1/8
P(B|A) = P(A⋂B) / P(A)
= 1/8 / 7/8
= 1/7

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