Sally is spinning a spinner with the numbers 1-8 with equal size sections. If she spins the spinner 1 time, what is the probability that she will land on a prime number? Also, find the complement of this event.

1 Answer
May 1, 2018

#P(2,3,5 or 7) = 1/2# (Probabilty of landing on a prime number)
#P_c = 1 - 1/2 = 1/2# (Probability of not landing on a prime)


(Assuming 1-8 means both are included)

There are 4 primes in the list, out of a total 8 numbers. Thus the probability is the number of favourable outcomes(4) divided by total possible outcomes(8). This equals one-half.

The probability of the complement of any event is #P_c = 1 - P_1#.
The complement of the prime set is #{1, 4, 6, 8}# This is not the set of composite numbers(as 1 is considered neither prime nor composite). Thus the complement is the set of non-prime numbers from 1 to 8.

#E_2 = # Landing on a non-prime number