Answer:
A. T > 2.539
Step-by-step explanation:
We have a hypothesis test of the mean, with unknown population standard deviation.
The hypothesis are:

From the hypothesis we can see that the test is right-tailed, so the critical value of t should be a positive value.
The degrees of freedom can be calculated as:

The significance level is 0.01, so the critical value tc should be the one that satisfies:

Looking up in a t-table, for 19 degrees of freedom, this critical value is tc=2.539.
Answer:
D
Step-by-step explanation:
(2x + 2) -
(3x - 1) = 15
multiply through by 4 ( the LCM of 2 and 4 ) to clear the fractions
2(2x + 2) - (3x - 1) = 60 ← distribute parenthesis and simplify left side
4x + 4 - 3x + 1 = 60
x + 5 = 60 ( subtract 5 from both sides )
x = 55
Answer :
27.5 minutes
Steps:
1) put into fraction form:
160/20 = 220/x
2) simplify:
160/20 = 8/1
3) cross multiply:
8 • x = 8x
220 • 1 = 220
4) divide on both sides:
8/8 = crosses out
220/8 = 27.5