The standard deviation is 3 , so 50 -47 = 3, means the 47 candies is 1 deviation below the mean.
A normal distribution, 68% of the sample falls within 1 standard deviation, which means 100-68 = 32 is out side the mean. Half of that, 32 / 2 = 16% is above and the other half (16%) would be below.
12 bags were below, so we would do a ratio, with the percentages as a whole number, so 16% = 16 and 100% = 100:
12/16 = X/100
Cross multiply: 16x = 1200
Divide both sides by 16:
X = 1200/16
X = 75
The answer is 75 bags were tested.
