There are 7 math books, 9 science books and 5 literature books. Student has to select 2 books from each set.
This is a combination problem.
Number of ways to select 2 math books from 7 books = 7C2 = 21
Number of ways to select 2 science books from 9 books = 9C2 = 36
Number of ways to select 2 literature books from 5 books = 5C2 = 10
Total number of ways to select 2 books from each set = 21 x 36 x 10 = 7560 ways.
So there are 7560 ways to select 2 books from each set of seven math books, nine science books, and five literature books
A=8
B=10
Hope this helps :D
Answer:
a. 19.68 miles per gallon.
b. 26.32 miles per gallon.
Step-by-step explanation:
Mean gas mileage (μ) = 23.0 mpg
Standard deviation (σ) = 4.9 mpg
In a normal distribution, for any length X, the z-score is determined by the following expression:

In a normal distribution, the 25th percentile (first quartile) of a normal distribution has a corresponding z-score of z = -0.677 and the 75th percentile has a corresponding z-score of z = 0.677
a. The first quartile of the distribution of gas mileage is

19.68 miles per gallon.
b. The third quartile of the distribution of gas mileage is

26.32 miles per gallon.
Sorry I am a little late...
a = -2
b = -9
Here is how to solve the problem.
First thing I did was multiply the first equation by -2 so that we can eliminate the the b. After you multiply it by -2, your new equation is -16a + 8b = -40.
You leave the second equation alone and all you do is combine like terms. So -16a+5a is -11. And you eliminate the b. Then you're going to do -40+62 which is 22. So it's -11a=22 and then you have to solve for a. What I did was I multiplied the whole thing by minus to turn the a positive. So then it's 11a=-22. Pretty easy, the final step is to simplify. -22/11 is -2. ;D
So there you have your first answer.
a = -2
Now we're going to use the first answer to help us find b.
For the second equation, all you're going to do is plug in that a.
5 (-2)-8b=62
-10 - 8b = 62
Now we move the -10 to the other side...
-8b = 62 + 10
-8b = 72
Multiply the whole thing by negative once again to turn the b positive.
Now we have 8b = -72
The final step is to simplify. -72/11 = -9
b = -9
Hope this makes sense! Also I had the same question on my test and I got it right. :)