If r follows normal distribution, graph ROE probability distribution for D/E = 0, 1, 5, 10.

Some equations given as guides:

ROE = (rD/E + rE/E iD/E)(1-t)

= [r + (r i) D/E] (1-t)

Variance (ROE) = Var(r)(1+D/E)2 (1-t)2