Qa - binomial distributions - q3

If X follows normal distribution with mean = 50, and SD=10, what is the value of P(X<=60/ X>50).

a) 0.8413 b) 0.6828 c) 0.1587 d) 0.7256

Thanks in advance.

P(A|B) = P(AintB)/P(B) so given probability is P(50<X<60)/P(X>50) P(X>50) is 0.5 and 60 = 50 +10 = mean + 1 standard deviation 68% of values lie between 40 and 60 so 34% lie between 50 and 60(due to symmetry) so 0.34/0.5 = 0.68 is the ans(approx) so b is the answer

Thanks..