Question

for a population of 800000 subway riders, the numbers of subway trips taken per rider last january are approximately normally distributed with a mean of 56 trips and a standard deviation of 13 trips. approximately how many of the riders took between 30 and 43 trips last january??? ...?

Answer 1

So, we have
Z=x−μ / σ

Mean would be = 56
  30 - 56 = |-26| 4
3 - 56 = |-13|
 and
Standard deviation= 13
2 - 1 will give us the approximate area
  95/2 - 68/2 = N

   95 -68 = 27

 27 /2 = 13.5
Hence, the answer would be
800,000 * .135
=  108000