Question

A recent article in the paper claims that government ethics are at an all-time low. Reporting on a recent sample,

Answer 1

Answer:

Probability that more than eight but fewer than 12 of the 20 constituents sampled believe  their representative possesses low ethical standards is 0.417890.

Step-by-step explanation:

We are given that the paper claims that 43% of all constituents believe their representative possesses low ethical standards.

Suppose 20 of a representative's constituents are randomly and independently sampled.

The above situation can be represented through binomial distribution;

$P(X=r) = \binom{n}{r} \times p^{r} \times (1-p)^{n-r} ; x = 0,1,2,3,.....$

where, n = number of trials (samples) taken = 20 constituents

            r = number of success = more than eight but fewer than 12

            p = probability of success which in our question is probability that

                  all constituents believe their representative possesses low

                  ethical standards, i.e; p = 43%

Let X = Number of constituents who believe their representative possesses low ethical standards

So, X ~ Binom(n = 20 , p = 0.43)

Now, Probability that more than eight but fewer than 12 of the 20 constituents sampled believe  their representative possesses low ethical standards is given by = P(8 < X < 12)

P(8 < X < 12)  =  P(X = 9) + P(X = 10) + P(X = 11)

= $\binom{20}{9} \times 0.43^{9} \times (1-0.43)^{20-9}+ \binom{20}{10} \times 0.43^{10} \times (1-0.43)^{20-10}+\binom{20}{11} \times 0.43^{11} \times (1-0.43)^{20-11}$

= $167960 \times 0.43^{9} \times 0.57^{11}+ 184756 \times 0.43^{10} \times 0.57^{10}+167960 \times 0.43^{11} \times 0.57^{9}$

= 0.417890

Hence, the required probability is 0.417890.