Question: Chapter 5: Uniform Distribution (Concepts), Uniform Distribution
Score: 9/24 Answered: 5/8
Question 6
The round off errors when measuring the distance that a long jumper has jumped is uniformly distributed
between 0 and 5.6 mm. Round values to 4 decimal places when possible.
a. The mean of this distribution is
b. The standard deviation is
c. The probability that the round off error for a jumper's distance is exactly 2.8 is P(x = 2.8) =
d. The probability that the round off error for the distance that a long jumper has jumped is between
1.9 and 5.5 mm is P(1.9 < x < 5.5) =
e. The probability that the jump's round off error is greater than 4.02 is P(x > 4.02) =
f. P(x > 3.3 | x > 0.4) =
g. Find the 54th percentile.
h. Find the minimum for the upper quartile.
Hint:
Written Hint
Helpful Videos: Probability, Conditional Probability, Conditional Probability, Percentiles
The graph is a uniform distribution question with a rectangular/flat density over the interval from 0 to 5.6, positioned at center.
1. **Problem Statement:**
We have a uniform distribution for round off errors between $0$ and $5.6$ mm.
2. **Uniform Distribution Basics:**
For a uniform distribution $U(a,b)$:
- Mean $\mu = \frac{a+b}{2}$
- Variance $\sigma^2 = \frac{(b-a)^2}{12}$
- Standard deviation $\sigma = \sqrt{\sigma^2}$
- Probability density function (pdf) $f(x) = \frac{1}{b-a}$ for $a \leq x \leq b$
- Probability for an interval $P(c < X < d) = \frac{d-c}{b-a}$
- Probability at a single point $P(X=x) = 0$ for continuous distributions
- Percentile $P_p = a + p(b-a)$ where $p$ is the percentile in decimal form
3. **Given:** $a=0$, $b=5.6$
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4. **a. Mean:**
$$\mu = \frac{0 + 5.6}{2} = \frac{5.6}{2} = 2.8$$
5. **b. Standard Deviation:**
$$\sigma = \sqrt{\frac{(5.6 - 0)^2}{12}} = \sqrt{\frac{5.6^2}{12}} = \sqrt{\frac{31.36}{12}} = \sqrt{2.6133} = 1.6166$$
6. **c. Probability at exactly $2.8$:**
For continuous uniform distribution,
$$P(x=2.8) = 0$$
7. **d. Probability between $1.9$ and $5.5$:**
$$P(1.9 < x < 5.5) = \frac{5.5 - 1.9}{5.6 - 0} = \frac{3.6}{5.6} = 0.6429$$
8. **e. Probability greater than $4.02$:**
$$P(x > 4.02) = \frac{5.6 - 4.02}{5.6 - 0} = \frac{1.58}{5.6} = 0.2821$$
9. **f. Conditional Probability $P(x > 3.3 | x > 0.4)$:**
$$P(x > 3.3 | x > 0.4) = \frac{P(x > 3.3)}{P(x > 0.4)} = \frac{\frac{5.6 - 3.3}{5.6}}{\frac{5.6 - 0.4}{5.6}} = \frac{2.3/5.6}{5.2/5.6} = \frac{2.3}{5.2} = 0.4423$$
10. **g. 54th Percentile:**
$$P_{54} = 0 + 0.54 \times (5.6 - 0) = 0.54 \times 5.6 = 3.0240$$
11. **h. Minimum for the upper quartile (75th percentile):**
$$P_{75} = 0 + 0.75 \times (5.6 - 0) = 0.75 \times 5.6 = 4.2000$$
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**Final answers:**
- a. Mean = $2.8$
- b. Standard deviation = $1.6166$
- c. $P(x=2.8) = 0$
- d. $P(1.9 < x < 5.5) = 0.6429$
- e. $P(x > 4.02) = 0.2821$
- f. $P(x > 3.3 | x > 0.4) = 0.4423$
- g. 54th percentile = $3.0240$
- h. Minimum for upper quartile = $4.2000$