# Math Help - posibilitys

1. ## posibilitys

For year 8 students, 20% have a shoe size greater than 10.5, but 95% have a shoe size less than 11.5. What is the chance of a year 8 student having a shoe size:
a. less than or equal to 10.5
b.11.5 or greater
c.between 10.5 and 11.5

i really dont know how to find the chances, please can someone explain to me how to do it??

2. Originally Posted by kl050196
For year 8 students, 20% have a shoe size greater than 10.5, but 95% have a shoe size less than 11.5. What is the chance of a year 8 student having a shoe size:
a. less than or equal to 10.5
b.11.5 or greater
c.between 10.5 and 11.5

i really dont know how to find the chances, please can someone explain to me how to do it??
You're given $\Pr(X > 10.5) = 0.2$ and $\Pr(X < 11.5) = 0.95$.

a. $\Pr(X \leq 10.5) = 1 - \Pr(X > 10.5)$.

b. $\Pr(X \geq 11.5) = 1 - \Pr(X < 11.5)$.

c. $\Pr(10.5 < X < 11.5) = \Pr(X < 11.5) - \Pr(X < 10.5)$.

3. Originally Posted by mr fantastic
You're given $\Pr(X > 10.5) = 0.2$ and $\Pr(X < 11.5) = 0.95$.

a. $\Pr(X \leq 10.5) = 1 - \Pr(X > 10.5)$.

b. $\Pr(X \geq 11.5) = 1 - \Pr(X < 11.5)$.

c. $\Pr(10.5 < X < 11.5) = \Pr(X < 11.5) - \Pr(X < 10.5)$.

i dont get it

4. Originally Posted by kl050196
i dont get it
Be specific - what don't you get?