Weights of apples grown in an orchard are known to follow a normal distribution with mean 160 grams. It is known that approximately 99.7% of apples have weights between 124 and 196 grams. What is the standard deviation of weights of all apples grown in the orchard?

I get 12 grams as the standard deviation. It is following the 68-95-99.7 normal distribution. So 99.7% is 3 standard deviations away.

With a mean of 160, and 3 standard deviations away is 196 or 124. Both of which are 36 grams away.

So 36 divided by 3 is 12 grams.