A cell phone company offers a simple extended warranty plan. If your phone is damaged, they will repair it for up to $50. If you lose or destroy your phone, they will give you a $200 voucher towards a new phone. The company believes that 5% of customers will need the replacement voucher and 10% will request a repair.
What is the standard deviation of the 10 total warranty plans? What assumption does this calculation require? Do you think this assumption is reasonable?