The sum of 5/21 and 4/7 by their difference ​

What is the area of triangle abc if a = 8, b = 11, and c = 15?

This is different from the first one can someone me

He weights of 2-pound bags of best dog food are approximately normally distributed with a given mean  and standard deviation  according to the empirical rule, what percentage of the bags will have weights within 3 standard deviations of the mean? 47.5%68%95%99.7%