How to calculate percent from standard deviation and mean?

Question

The daily protein intake of children aged 11-15 in a rural community follows a normal distribution with a mean of 27 grams and a standard deviation of 7 grams. What percent of these children get less than 13 grams of protein per day? 

Answer 1

The mean is 27 and the sd is 7 and it's a normal distribution. This tells us that 68% of the data falls within one sd of the mean and 95% falls within 2 sd of the mean.

 

27 - (2*7) gives us 13, and they want to know what percent is below 13. Since 95% falls within 2 sd of the mean, 5% falls outside of 2 sd. Since this is distributed normally, 2.5% would get less than 13 grams.