-2 or 2 either one
Hope this helps
Δx (delta x) is about a secant line, a line between two points representing the rate of change between those two points. That's a "differential" (between the two points).
dx is about a tangent line to one point, representing an instantaneous rate of change. That makes it a "derivative."
We are given with
x1 = 20 min
s1 = 2 min
x2 = 30 min
s2 = 4 min
p = 0.9
Condition (x > 25)
We need to get the t-value between the two means and comparing it wit the t-value for the time of 25 minutes given that there is a 90% probability that the weather will be good. Simply use the t-test formula and use the t-test table to get the probability.
