the time required for an oil chnage at jiffy lube is approximately normally distrubed, with an average time for $17$ minutes and a standard deviation for $2\mathrm{.}5$ minutes. jiffy lube guarantees that the service will taj eno longer than $20$ minutes. if it does take lomger, the customer recieves the service for half price. what percent of customers will reivve this deal? if jiffy lube does not wnt to give the discount to more than $3$ percent of it customers, ho wlong should it make the guareanteed time limit$?$