assume normal distribution of data has a mean of12 and a standard deviation of 3find the %age value below 12?

Question

Use the 68-95-99.7 rule

Answer 1

I'm not sure what your question is asking. Are you asking what percentage of the data is below a value of 12? Since you have a normal distribution with a mean of 12, exactly 50% of the data is below 12. You don't need to use any other rules.

Answer 2

If the mean is 12 then the %ge below 12 is 50!

the 68-97-99.7 is the amount between +- standard deviations.

68% lies between +- 1 deviation i.e. 9 and 15 with 34% lying between 9 and 12 and 34% between 12 and 15