Question

P( | x | ? x1 | ND: ? = 200, ? = 10) = .40

What is x1?

		2.5
		5.2
		6.5
		8.4
		12.8

Answer 1

Given P( | x | ? x1 | ND: ? = 200, ? = 10) = .40

1 - P( | x | ? x1 | ND: ? = 200, ? = 10) = 1 -0.40

P( | x | < x1 | ND: ? = 200, ? = 10) = 0.60

P(-x1 < X< x1 | ND: ? = 200, ? = 10) 0.60

P( (-x1 -200)/10 < Z <  (x1 -200)/10 ) = 0.60

As per standard normal table, P(-0.8416 <Z< 0.8416) = 0.60

Therefore, (x1 -200)/10 = 0.8416

x1 - 200 = 8.416

x1 = 208.416

similiary (-x1 -200)/10 = -0.8416

-x1 - 200 = -8.416

-x1 = 191.584

Correct answer: Option (D) 8.4