Assume the random variable x is a normal distribution with the mean=81 and the standard deviation sigma =5
P(x<77)
step 1
Find out the z-score
we have that
Z score =(x - μ)/σ
is given
x=77
μ=81
σ=5
substitute
Z-score=(77-81)/5
Z-score=-0.8
using a z-score probability calculator or tables
Probability of x<77:
P=0.2119