I want to take a picture of my six friends standing in two horizontal rows of three. How many different photos can I take if the tallest person must stand in the back row, the shortest person must stand in the front row, and two of my friends are identical twins whom I can't tell apart? (The identical twins are neither the tallest nor the shortest.)
This may be incorrect, but I'll give it a try.
The tallest person is in the back row, with three spots. 3 ways to place him. The shortest person stays in the front row, 3 ways to place him. Normally, our answer would just be 3*3*4! (4! means 4*3*2*1) but two friends are identical twins, so they are indistinguishable. Therefore our answer is (3*3*4!)/(2!) = 108.
Hope this helped!