Statistic Questions

Hi. If anybody could help with these stats q's then it would be greatly appreciated!

Q1) Thin-film resistors in a hybrid circuit, with a mean value of 1 kilo-ohm, are rejected if their resistance is less than 900 ohm or greater than 1.1 kilo-ohm. It is found that, in a large batch, 2.5% are rejected as too high and 2.5% are rejected as too low. Assuming that the resistance values are normally distributed, calculate the percentage rejected if the limits are changed ti 950ohms and 1.15kilo-ohms.

** I believe that the above Q requires the reverse use of normal distribution tables **

Q2) Capacitors with a nominal value of 12.5 micro-farads are selected on test for use in an oscillator circuit. Capacitance values in the range 12.45 micro-farads to 12.55 micro-farads are acceptable for use. Records show that 2.5% are rejected as too low and 5% are rejected as too high. Calculate to three d.p. the mean and standard deviation of these components.

** I believe that this requires the use of simultaneous equations **

Reply 1

Zacken

Original post by JordanSHowarth

X ~ N(1, sigma).

P(X > 1.1) = 2.5/100 (use percentage points)
P(X < 0.9) = 2.5/100

You should be able to find the variance from that.

Then compute P(X > 1.15) and P(X < 0.95).