Hello tutors,

Please help me with this question.

A tire manufacturer believes that the treadlife of its snow tires can be described by a Normal model with a mean of 32,000 miles and standard deviation of 2500 miles.

what fraction of these tires can be expected to last between 30, 000 and 35,000 miles? *Estimate the IQR of the treadlives. How can i estimate it?

* In planning a marketing strategy, a local tire dealer wants to offer a refund to any customer whose tires fail to last a certain number of miles. However, the dealer does not want to take too big a risk. If the dealer is willing to give refunds to no more than 1 of every 25 customers, for what mileage can he guarantee these tires to last?

Thanks..