**Answer:**

**1/4**

**Step-by-step explanation:**

Let's denote the probabilities as following:

Probability that a teenager has a sister:

**P(A) = 12/28**

Probability that a teenager has a brother:

**P(B) = 7/28**

Probability that a teenager has both a sister and a brother:

**P(A⋂B) = 3/28**

Probability that a selected teenager has a sister also has a brother, or in other words, he/she has a brother, given he/she had a sister:

**P(B|A)**

Let's apply the formula of conditional probability to work out **P(B|A)**

**P(B|A) = P(A⋂B)/P(A) = (3/28)/(12/28) = (3*28)/(12*28) = 3/12 = 1/4**

**=> Option C is correct**

**Hope this helps!**

X+(x+1)=17

So 2x+1=17

Which means 2x=16

Which then means x=8

But you still need the second number, which is x+1, so 8+1=9.

This means that the consecutive numbers are 8 and 9.

If she rides at 12 miles per hour, we know that 45 minutes is three quarters of an hour, therefore just workout:

3/4 x 12 = 9

So she would travel 9 miles in 45 minutes.

To obtain a more accurate answer! :)