An english professor determined the mean of her final exam scores to be 78 with a standard deviation of 6.3. find the minimum and maximum “usual” values of the test scores. 65.4 and 90.6 69.7 and 86.3 71.7 and 84.3 59.1 and 96.9

The minimum and maximum usual value of the test scores are:

              65.4 and 90.6

We know that:

The maximum usual value is two standard deviations above the mean and the minimum usual value is two standard deviation below the mean.

i.e.

Maximum value= Mean+2×standard deviation.

i.e.   Maximum value= 78+2×6.3

Maximum value= 90.6

and

Minimum value= Mean-2×standard deviation.

Minimum value= 78-2×6.3

i.e. Minimum value= 65.4

a.

step-by-step explanation:

step 1 distribute 2 to every term in the parentheses

step 2 add 10 on both sides of the equal sign