Triangle ACD consists of AC, AD and CD.

Because AD is the center line of triangle ABC.

So CD = BD

So the difference between the perimeters of triangle ABD and triangle ACD is 5-3 = 2 cm.

(2) Because the area of triangle ABD is 1/2*AE*BC.

The area of triangle ACD is 1/2*AE*CD.

And because BC=2CD.

So the area of triangle ABD is twice that of triangle ACD.