A student has a class with four tests, each worth 100 points, and has earned these scores on the first three tests: 75, 74, 71. What is her average now? What score must
she earn on the fourth test to get a B (80) in the class?

average = 52, 100 on fourth test

Step-by-step explanation:

average = 75 + 74 + 71 =  156 / 3 = 52

average = 52

b grade = 75 + 74 + 71 + 100 = 320 / 4 = 80

to get a b grade she must get 100 on her fourth test

85.560%

step-by-step explanation:

conditional probability is defined as:

p(a|b) = p(a∩b) / p(b)

in other words, the probability that a occurs, given that b has occurred = the probability that both a and b occur / the probability that b occurs.

in this example:

p(turns 64 | turns 44) = p(turns 64 & turns 44) / p(turns 44).

if someone turns 64, they must have already turned 44, so:

p(turns 64 | turns 44) = p(turns 64) / p(turns 44)

on page 42, we see that of the original 100,000, 94944 turn 44, and 81234 turn 64.   therefore:

p(turns 64 | turns 44) = 81234 / 94944

p(turns 64 | turns 44) = 0.85560