A company installs 5000 light bulbs, each with an average life of 500 hours, standard deviation of 100 hours, and distribution approximated by a normal curve. Find the percentage of bulbs that can be expected to last the period of time. Less than 690 hours.
A. 97.06%
B. 47.14%
C. 97.1%
D. 97.2%

Question

A company installs 5000 light bulbs, each with an average life of 500 hours, standard deviation of 100 hours, and distribution approximated by a normal curve. Find the percentage of bulbs that can be expected to last the period of time. Less than 690 hours.
A. 97.06% 	
B. 47.14% 	
C. 97.1% 	
D. 97.2%

anonymous · Answer

97.13% confirmation for above
AP stat this year

anonymous · Answer

here z=(690-500)/100 thus z=1.9 area on the left of z =1.9 is 0.5+.4713 =.9713 (or 97.13% )
 so its B 47.14%