The number of pieces of popcorn in a large movie theatre popcorn bucket is normally distributed, with a mean of 1720 and a standard deviation of 20. Approximately what percentage of buckets contain between 1680 and 1760 pieces of popcorn? (1 point)
Incorrect

Approximately 68%

Approximately 75%
Correct
answer

Approximately 95%

99.7%

I get the -2 and 2 but I don't understand exactly to get the percentage of z score