Answer: 29/48
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Step-by-step explanation:
There are 17 people under age 25.
There are 17 people that got a B.
17+17 = 34 people so far in either group. However, notice that we double-counted the people who are both under 25 and got a B. There are 5 such people we double-counted here.
Subtract off 5 to correct for this erroneous double-counting
34-5 = 29
There are 29 people who either...
- are under 25
- got a B
- are both under 25 and got a B
This is out of 48 people total.
To arrive at the probability we want to find, divide the two values we found: 29/48
Optionally you can convert that fraction to decimal form, but I think it's better to stick with the fraction (since it's most exact).