in how many ways can five airplanes line up for departure on

Solution

5! ways=120 ways

Since The above problem is similar to arrangement of flights on runway one after the other,

The first plane is placed in any of the five positions in 5 ways.

After placing that, the second plane is placed in remaining 4 positions in 4 ways

3rd plane in 3 ways, 4th plane in 2 ways , last plane in only way.

So they can be arranged in 5*4*3*2*1 ways = 120 ways