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Consider a collection of envelopes consisting of 3 red envelopes, 2 blue envelopes, 3 green envelopes, and 1 yellow envelope. If three envelopes are selected at random, without replacement, determine the probability that they are all red envelopes.

The probability that all of the envelopes are red is $\square$.
(Type an integer or a simplified fraction.)

Step 1 ：Consider a collection of envelopes consisting of 3 red envelopes, 2 blue envelopes, 3 green envelopes, and 1 yellow envelope. If three envelopes are selected at random, without replacement, determine the probability that they are all red envelopes.

Step 2 ：Calculate the probability by multiplying the probability of drawing each red envelope one after the other. The probability of drawing the first red envelope is \( \frac{3}{9} \), the second is \( \frac{2}{8} \), and the third is \( \frac{1}{7} \).

Step 3 ：The probability that all of the envelopes are red is \( \frac{3}{9} \times \frac{2}{8} \times \frac{1}{7} = 0.011904761904761904 \).

Step 4 ：Simplify the final answer to a fraction.

Step 5 ：Final Answer: The probability that all of the envelopes are red is \( \boxed{\frac{1}{84}} \).