A
B
C
D
E
$$? = C\left( {10,2} \right) \cdot C\left( {8,2} \right) = \left( {\frac{{10 \cdot 9}}{2}} \right) \cdot \left( {\frac{{8 \cdot 7}}{2}} \right) = 45 \cdot 28 = \underleftrightarrow {45 \cdot \left( {30 - 2} \right) = 1350 - 90} = 1260$$BTGmoderatorDC wrote:10 different biology books and 8 different chemistry books lie on a shelf. In how many ways can a student pick 2 books of each type?
A. 80
B. 160
C. 720
D. 1100
E. 1260
Source: Economist Gmat
Take the task of selecting 4 books and break it into stages.BTGmoderatorDC wrote:10 different biology books and 8 different chemistry books lie on a shelf. In how many ways can a student pick 2 books of each type?
A. 80
B. 160
C. 720
D. 1100
E. 1260
Since the order in which the books are selected does not matter, we have a combination problem. Let's start by determining the number of ways to select the biology books.BTGmoderatorDC wrote:10 different biology books and 8 different chemistry books lie on a shelf. In how many ways can a student pick 2 books of each type?
A. 80
B. 160
C. 720
D. 1100
E. 1260
OA E
Source: Economist Gmat
