What is the probability that the student gets at least 13 questions right? First, draw the histogram and shade the desired area. 0.20 B 10 13 Histogram; X binomial; mean-10, s.d.-2.24 Curve: normal X; mean=10, s.d.=2.24 We can see that the bars for 13 and greater are shaded. The shading actually starts at This is the continuity correction. To find the probability using the normal table (opens in a new window), find the z-score for 12.5. 12.5-10 2.24 (Always round to z-scores to the nearest hundredth.) P(T Binomial 2 13) ~ P(T Normal 2 12.5) = P(: 2 1.12) = (Click to view hint) Let's see how close this is to the actual binomial probability. P(x 2 13) = 20 13(0.5) 13(0.5)7 + 20 C'14 (0.5) 14(0.5)6 + 20 C15 (0.5) 15(0.5)5 + 20 C16(0.5) 16(0.5)" + 20 C'17(0.5) 17 (0.5)3 + 20 C'18 (0.5) 18(0.5) 2 + 20 CIs (0.5)19(0.5)1 + 20 20 (0.5) 20 (0.5) = 0.1316 It turns out that the exact probability in this case is 0.1316, so the approximation is excellent. Check