Exercise 2:

Samples of two types of electric light bulbs were tested for

length of life and following data were obtained:

Type I

Type II

Sample No.

n

1

= 8

n

2

= 7

Sample Means

x

1

= 1,234 hrs.

x

2

= 1,036 hrs.

Sample SD's

s

1

= 36 hrs.

s

2

= 40 hrs.

Is the difference in the means sufficient to warrant that type I is superior

to type II regarding length of life?