Normally distributed random variable and probability

major_maths

1. Homework Statement
The top-selling Red and Voss tire is rated 60000 miles, which means nothing. In fact, the distance the tires can run until wear-out is a normally distributed random variable with a mean of 70000 miles and a standard deviation of 5000 miles.

A: What is the probability that the tire wears out before 60000 miles?
B: What is the probability that a tire lasts more than 79000 miles?

2. Homework Equations
z = (Y-μ)/σ

3. The Attempt at a Solution
I plugged the values into the above equation and got z=-2. Looking at the chart in my book, Pr(z=2)=0.0228 and I figured this should work since z is 2 standard deviations from the mean no matter whether it's positive or negative. When I submitted 0.0228 though, the answer was incorrect.

Related Calculus and Beyond Homework Help News on Phys.org

Ray Vickson

Homework Helper
Dearly Missed
1. Homework Statement
The top-selling Red and Voss tire is rated 60000 miles, which means nothing. In fact, the distance the tires can run until wear-out is a normally distributed random variable with a mean of 70000 miles and a standard deviation of 5000 miles.

A: What is the probability that the tire wears out before 60000 miles?
B: What is the probability that a tire lasts more than 79000 miles?

2. Homework Equations
z = (Y-μ)/σ

3. The Attempt at a Solution
I plugged the values into the above equation and got z=-2. Looking at the chart in my book, Pr(z=2)=0.0228 and I figured this should work since z is 2 standard deviations from the mean no matter whether it's positive or negative. When I submitted 0.0228 though, the answer was incorrect.
Your answer is correct. Who told you it is incorrect?

RGV

major_maths

It's an online homework assignment. I talked to my teacher and he said the site was having issues with the rounding. Thanks for the help!

Physics Forums Values

We Value Quality
• Topics based on mainstream science
• Proper English grammar and spelling
We Value Civility
• Positive and compassionate attitudes
• Patience while debating
We Value Productivity
• Disciplined to remain on-topic
• Recognition of own weaknesses
• Solo and co-op problem solving