A sample survey interviews an SRS of 267 college women. Suppose (as is roughly true) that 70% of all college women have been on a diet within the past 12 months. Use a Normal approximation to find the probability that 75% or more of the women in the sample have been on a diet.
The Attempt at a Solution
I could do this if I knew how to find the standard deviation, but I don't..
Any help would be great, thanks!