1. The problem statement, all variables and given/known data The random variable X is normally distributed. The values 650 and 850 are at the 60th and 90th percentile of the distribution of X respectively. Find the value of the 75th percentile of the distribution of X. 2. Relevant equations I found the above formula from internet. where sigma is standard deviation, mu is mean 3. The attempt at a solution I dont know the values of mu, sigma and Z. Somebody please guide me. Zulfi.