Question

A spinner is divided into sections shaded either black or gray. The probability that the spinner will stop on a black section is 20 percent.

What is the probability that the spinner will stop on a gray section?

A.
20%

B.
40%

C.
60%

D.
80%

Answer 1

kc_kennylau

Answer 2

1 - 20%

Answer 3

Because it's either black or gray

Answer 4

So P(black) + P(gray) = 1

Answer 5

Get it?

Answer 6

no

Answer 7

P(something) means probability of something

Answer 8

P(A or B) = P(A) + P(B)
P(A and B) = P(A) * P(B)

Answer 9

These two formulas will be very useful

Answer 10

It's either black or gray, so P(black or gray) = 1 because it must happen

Answer 11

Anything that "must happen" will have a probability of 1

Answer 12

Get it?

Answer 13

Do you understand why P(black or gray)=1

Answer 14

yes

Answer 15

P(black or gray)=1
Therefore P(black) + P(gray) = 1
Do you understand this

Answer 16

kinda

Answer 17

those are complimentary events.

Answer 18

Because P(A or B) = P(A)+P(B)

Answer 19

Therefore P(black or gray) = P(black) + P(gray)

Answer 20

Therefore P(black) + P(gray) = 1

Answer 21

Now you have P(black)=20%

Answer 22

Substitute P(black)=20% to P(black)+P(gray)=1

Answer 23

Understand?

Answer 24

i think

Answer 25

Then do it

Answer 26

probability of wheel to stop at black is 20%. so what if doesnt stop on black .. it stops on grey .. it means its probability become rest of 100. that is 100-20 = 80

Answer 27

ohhh now i understand

Answer 28

Glad you understand, because we gave no explanation to the questions before this

Answer 29

so the ans id 80

Answer 30

Yes

Answer 31

@kc_kennylau tried very hard to make you @72595210002 understand .. i give him my medal.

Answer 32

Thanks