Suppose compact fluorescent light bulbs last, on average, 10,000 hours. the standard deviation is 500 hours. what percent of light bulbs burn out within 11,000 hours?
how do you show your work for this problem. i dont know how to solve it.

Arley is building a model of a city map. in one part of the city, three roads form a right triangle, which harley draws as triangle abc, with the following measures: m∠b=90° and m∠a=30°. in his scale model, the hypotenuse of triangle abc, ac¯¯¯¯¯¯¯¯, has a length of 817−−√ cm. what is the value of a (the length of bc¯¯¯¯¯¯¯¯)?

Which expression is equal to (21)(7)(3x) using the associative property? (21 · 7 · 3)x (7)(21)(3x) 32(7 + 3x) (3x)(7)(21)

35 ! insert < , > , or = to make the sentence true. 12 __ 25 > =