Question

the table shows the movement of walt disney stock for 30 randomly selected trading days. “up” means the stock price increased in value for the day. “down” means the stock price decreased in value for the day, and “no change” means the stock price closed at the same price it closed for the previous day. complete parts (a)-(e) below. down down down down up up down up up up down up down down up up down up down up down up down down no change up down down no change no change 0.400 (round to the nearest thousandth as needed.) (d) is it unusual for walt disney stock to decrease in value for the day? it is unusual because for every 100 days, we can expect about of those days to show “down.” (round to the nearest integer as needed.)

Explanation:

Step1: Count number of "Down" days

First, count the number of "Down" days in the 30 - day sample. After counting, assume the number of "Down" days is $n$. Let's say we count and find $n = 15$.

Step2: Calculate probability of "Down" day

The probability $P$ of a "Down" day in the sample is calculated as $P=\frac{n}{30}$. Substituting $n = 15$, we get $P=\frac{15}{30}=0.5$.

Step3: Estimate number of "Down" days in 100 - day period

To estimate the number of "Down" days in 100 days, we use the proportion. Let $x$ be the number of "Down" days in 100 days. Then $\frac{x}{100}=\frac{n}{30}$. Cross - multiplying gives $x=\frac{100n}{30}$. Substituting $n = 15$, we have $x=\frac{100\times15}{30}=50$.

Step4: Determine if it's unusual

A probability of 0.5 or an expected 50 "Down" days out of 100 is not unusual. Usually, an event with a probability less than 0.05 (or 5 out of 100) is considered unusual.

Answer:

It is not unusual because for every 100 days, we can expect about 50 of those days to show "Down".