# Math Help - Finding The Indicated Probability

1. ## Finding The Indicated Probability

Hi,

I'm positing several questions(4) in one thread so that you can see the different types of problems I have to figure out, but I have to find the indicated probability, my teacher had me do it by writing an equation starting with x=, but if there's an easier method to doing this, I'd appreciate if someone would explain that. This is really confusing to me. You don't have to do all of the problems, but could someone do one problem, and explain it at least?

Problem I:

P(A)=0.6
P(B)=0.35
P(A or B)=? Otherwise known as x.
P(A and B)=0.2

Problem II:

P(A)=?
P(B)=0.44
P(A or B)=0.56
P(A and B=-0.12

Problem III:

P(A)=0.75
P(B)=?
P(A or B)=0.83
P(A and B)=0.25

Problem IV:

P(A)=8%
P(B)=33%
P(A or B)=41%
P(A and B)=?

Thank you
Isabel

2. Hello, stmsnyder1!

These problems are all of the same type.

You are expected to know this formula:

. . . $P(A\text{ or }B) \;=\;P(A) + P(B) - P(A\text{ and }B)$

Just plug in the given numbers and solve for the missing value.

Problem III

$P(A)=0.75 \qquad P(A\text{ or }B) =0.83 \qquad P(A\text{ and }B) = 0.25$

Find $P(B).$

$\text{Formula: }\;\underbrace{P(A\text{ or }B)}_{\downarrow} \;=\;\underbrace{P(A)}_{\downarrow} + \underbrace{P(B)}_{\downarrow} - \underbrace{P(A\text{ and }B)}_{\downarrow}$

. . . . . . . . . $0.83 \quad = \quad 0.75 \; + \; P(B) \;\;\; - \;\;\; 0.25$

Got it?

Yep, thanks