Question

The probability that a twelve-year-old has a brother or sister is 25%. supposed you survey 300 twelve-year-olds. about how many do you think will have a brother or sister?

set up a solve a proportion for this as well.

Answer 1

n(B U S) = 75

Step-by-step explanation:

P(E) =

Let 'B' be the event of having twelve year old brother

Let 'S' be the event of having twelve year old sister

given data P(BUS) = 0.25

given total survey n(survey) = 300

we have to find the value is n(BUS) =?

we will use probability definition we get, P( BUS) =

substitute given values, we will get solution

after cross multiplication , we get

n(BUS) = 0.25 X 300

n(BUS) = 75

Answer 2

75 twelve-year-olds will have a brother or sister

25% of 300 = 75

Explanation:

Step 1: Our output value is 300.

Step 2: We represent the unknown value with x

Step 3: From step 1 above, 300=100%.

Step 4: Similarly, x=25%

Step 5: This results in a pair of simple equations:

300=100% (1).

x=25% (2).

Step 6: By dividing equation 1 by equation 2 and noting that both the RHS (right hand side) of both

equations have the same unit (%); we have

300/x 100%/25%

Step 7: Again, the reciprocal of both sides gives

x/300 25/100

x=75

Therefore, $25% of 300 is 75