Twenty-five heat lamps are connected in a greenhouse so that when one lamp fails, another takes over immediately. (only one lamp is turned on at any time.) the lamps operate independently, and the lifetime of each has a mean 50 hours and a standard deviation of 4 hours.
if the greenhouse is not checked for 1,300 hours after the lamp system is turned on, what is the probability that a lamp will be burning at the end of the 1,300-hour period?

Mrs. julien’s and mrs. castillejo’s classes are selling cookie dough for a school fundraiser. customers can buy packages of macadamia nut chip cookie dough and packages of triple chocolate cookie dough. mrs. julien’s class sold 25 packages of macadamia nut chip cookie dough and 30 packages of triple chocolate cookie dough for a total of $221.25. mrs. castillejo’s class sold 5 packages of macadamia nut chip cookie dough and 45 packages of triple chocolate cookie dough for a total of $191.25. (a) write the system of equations that model the problem. be sure to explain which equation represents which situation. (b) find the cost of each type of cookie. show your work. (c) explain which method you used to solve the system and why you chose that method.