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.

What is the 12th term of b(n)=-4-2(n-1)

Express in the simplest form: (x^2+9x+14/x^2-49) / (3x+6/x^2+x-56)

Statements reasons 1. ab ? cd; ad ? bc 1. given 2. ac ? ac 2. reflexive property 3. ? adc ? ? cba 3. ? 4. ? dac ? ? bca; ? acd ? ? cab 4. cpctc 5. ? dac and ? bca are alt. int. ? s; ? acd and ? cab are alt. int. ? s 5. definition of alternate interior angles 6. ab ? cd; ad ? bc 6. converse of the alternate interior angles theorem 7. abcd is a parallelogram 7. definition of parallelogram what is the missing reason in step 3?