We know that:
Substituting known values, we have:
Total number of bulbs tested, N = 445
Number of bulbs that lasted more than 500 hrs, x = 316
Point estimate of bulbs that lasted more than 500 hrs = x/N = 316/445 ≈ 0.71 = 0.71*100 = 71%
Count the squares from one point to the end point. X=4, Y=2. Formula of a slope is y/x. 2/4 or 1/2.
