Finding Standard Deviation of Normal Distribution

A work-study engineer times a certain operation, and discovers that the average time it takes is 10 minutes, but on 15% of occasions it takes more than 13 minutes. Assuming that times for the operation follow a normal distribution, what is its standard deviation?

Look at the normal distribution table. the z value for 15% probability to the right side is …

Solution explains the steps in finding standard deviation of a normal distribution with the help of standardized normal distribution tables.