Probability X Mitigation A = Modified probability
Probability X Mitigation B = Modified probability
A: 0.4 X 0.5 = 0.2
B: 0.4 X 0.95 = 0.38

You must consider each mitigation separately. Once you've gone throughthe process for several types of mitigation, you can pick which onesyou feel are most important or provide the best return. (Of course,some mitigation measures will have overlapping effects. We're notputting that into this math.)

At any rate, adding mitigation measures produces modified ALEs:

Incident cost X Modified probability = mALE
A: $1,000,000 X 0.2 = $200,000
B: $1,000,000 X 0.38 = $380,000

So, in each case you've reduced your ALE.