Idon't understand the 30-60-90 or the 45-45-90 to solve for the whole shape

The human resources manager at a company records the length, in hours, of one shift at work, x. he creates the probability distribution below. what is the probability that a worker chosen at random works at least 8 hours? probability distribution px(x) 6 hours 7 hours 8 hours 9 hours 10 hours 0.62 0.78 пол

Write the summation to estimate the area under the curve y = 1 + x2 from x = -1 to x = 2 using 3 rectangles and right endpoints

Apackage of five erasers cost 0. $.39 at this rate how many how much would 60 erasers cost in dollars and cents