A traffic study of 2,500 vehicles that passed by a checkpoint showed that their speeds were normally distributed with a mean of 82.5 kph and a standard deviation of 11.5 kph. How many vehicles had a speed of more than 90 kph
"\\bar x = 82.5"
"\\sigma = 11.5"
"P(X>90)=1-P(X<90) \\\\\n=1-P(Z<\\frac{90-82.5}{11.5})"
"=1-P(Z<\\frac{90-82.5}{11.5}) \\\\\n=1-P(Z<0.652) \\\\\n=1-0.7427\\\\\n=0.2573"
25.73% of 2500 vehicles:
"2500 \\times 0.2573= 643"
Answer: 643 vehicles have a speed of more than 90 kph.
Comments
Leave a comment