9 first-year teachers and 21 experienced teachers attended a school staff meeting meeting. What percentage of the teachers in the meeting were first-year teachers?

5

10

15

20

25

30

35

40

45

50

55

you didn't give an question you just gave us a statement

135

step-by-step explanation:

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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.