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Explanation:
The vertical bar is a shorthand way of saying "Given".
Writing P(A | B) means "probability of A given B"
In this case, we are given that "color name with six letters", so we are 100% certain that whatever was picked has six letters in the color name. That rules out green (5 letters) and red (3 letters). We'll ignore these colors entirely.
Instead we focus on yellow, orange, and purple.
Add up the frequencies for these colors to get: 18 yellow + 10 orange + 14 purple = 42 total
Of that total, there are 14 purple, so....
14/42 = (1*14)/(3*14) = 1/3
represents the probability we're after.
There's a 1 in 3 chance of getting a purple skittle if we are told, or we know 100%, that whatever color we picked has 6 letters in the name.
Side note: 1/3 = 0.333 = 33.3% approximately.