[GMAT math practice question]

In how many ways can three boys and four girls line up in a row, if girls take the first and last positions?

A. 28
B. 120
C. 720
D. 1,440
E. 5,040
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The number of ways we can choose 2 girls from 4 to take the first and last positions is 4C2 = (4 x 3)/2! = 12/2 = 6. Once the two girls, say, A and B, are picked, there are two ways to switch them, since A can be the first position and B the last or B can be the first position and A the last. The 5 people in the middle can be arranged in 5! = 120 ways. Thus, the total number of ways we can arrange these 7 people so that the first and last positions are taken by girls is:

6 x 2 x 120 = 1,440

Answer: D
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