For y = 25, what is the estimated value of x, from the following data x 11 12 15 16 18 19 21 y 21 15 13 12 11 10 9

Answer 1

you have 7 points, and the slopes of the line segments joining them are
-6, -2/3, -1, -1/2, -1, -1/2

That does not bode well for trying to estimate x when y=25.
Just using the nearest slope of -6, x would be 11 + 4/-6 = 10 1/3
Using the average slope of the whole data set, x would be 10 1/5
Or, counting (11,21) as an outlier, that would give x = 9 1/3