There are 3 possibilities when choosing 1 of 3 books. There are 8 possibilities when choosing 1 of 8 books. Events are independent of each other so "and" would be to multiply. 3 × 8 = 24 possible combinations
You can also see by writing out the possibilities.. Say names of books are {A,B,C} and names of CD's are {1,2,3,4,5,6,7,8} A1, A2, A3, A4, A5, A6, A7, A8 B1, B2, B3, B4, B5, B6, B7, B8 C1, C2, C3, C4, C5, C6, C7, C8
If we need to find the hidden number, Which for simplicity's sake we will denote as "n", lets first write out the equation.
"2 x [n + (-3)] = 4"
We can work through this problem backwards. if we need two times the sum of "n" and (-3) to get to 4, the only number that can be multiplied by 2 to get a product of 4 is 2, so "n" + (-3) must equal 2. so, From here, we can figure out that since 5 + (-3) equals 2, "n" Must equal 5. so, if we plug in 5 for "n" the equation looks like this:
"2 x [5 + (-3)] = 4"
So, since the equation makes sense, the answer is, "n = 5"
