Out of a total of 10 college textbooks estimate the standard deviation of their ages if the oldest textbook is known to be 7.9 years old and the newest textbook is 1.3 years old.

Given that the maximum age of the textbook is 7.9 years and the minimum age of the textbook is 1.3 years.

Using the range rule, the standard deviation is estimated as,

S≈maximum−minimum/4

=7.9−1.3/4

=1.65

The required value of the approximate standard deviation is 1.65.

square root of 36/6 = 2.449489743

square root of 16/6 = 1.632993162

square root of 6 = 2.449489743

the answer is square root of 16/6 because the square root of 36/6 is the same answer as square root of 6 = 2.449489743

just sum

10 + 10 = 20