Question

An article in the Journal of Composite Materials describes the effect of delamination on thenatural frequency of beams made from composite laminates. Five such delaminated beams were subjected to loads, and the resulting frequencies were as follows (in Hz):

230.66, 233.05, 232.58, 229.48, 232.58
(a) Find a 90% two-sided CI on mean natural frequency. Round your answers to 2 decimal places.
(b) Do the results of your calculations support the claim that mean natural frequency is 235 Hz?
(A). _____________<= U<= _______________
(B). YES OR NO ?

Answer 1

(230.21 ; 233.13)

Explanation:

Given the data :

230.66, 233.05, 232.58, 229.48, 232.58

To calculate the 90% CI

WE obtain the mean and standard deviation of the sample data :

Mean of sample, ΣX /n = 1158.35/5 = 231.67

The standard deviation of the sample, s = 1.531 (Using calculator).

(The 90% Tcritical value, 2 sided, df = 4) = 2.132

The confidence interval, CI :

Mean ± Tcritical * s/√n

C.I = 231.67 ± (2.132 * (1.531/√5)

C. I = 231.67 ± 1.4597

(231.67 - 1.4597) ; (231.67 + 1.4597)

(230.21 ; 233.13)