In a company, amount of light bills follows normal distribution with σ = 60. 11.31% of customers pay bill less than 260. What is average amount of light bill?[P(z=1.21)=0.3869]

Distribution of height of 1000 soldiers is normal with mean 165 cm & standard deviation 15 cm. How many soldiers are of height between 138 & 198 cm?[P(z=1.8)=0.4641,P(z=2.2)=0.4861]

A random variable X has mean 10, variance 4 and unknown probability distribution. Find ‘c’ such that P{|X-10|≥c}<0.04.

Variate X takes values $-1,1,3,5$ with associate probability $\frac{1}{ 6 },\frac{1}{ 6 },\frac{1}{ 6 },\frac{1}{ 2 }$ . Then $\left\{\mathrm{P}\right|\mathrm{x}-3|\ge 1\}=$ _______. 

A random variable X has a mean 12, variance 9 and unknown probability distribution. Find $P(6<X<18)\ge$ ________.