In a ΔABC, ∠A = 100°, AD bisects ∠A and AD ⊥ BC, then, ∠B is equal to

Calculations:

In triangle ABC, ∠A = 100°. AD is a bisector of ∠A, thus implying that it divides ∠A into two equal parts so each part is 100°/2 = 50°.

Since AD and BC are perpendicular, we know that ∠ADB = 90°

(because the angle between a line and a line perpendicular to it is always 90 degrees).

Now, looking at triangle ADB (which is a right triangle), the sum of its interior angles is 180°. If we subtract ∠ADB (90°) and ∠BAD (50°) from 180°, then we'll get that ∠ACB = 180° - 90° - 50° = 40°.

Now in ΔABC 

∠A + ∠B + ∠C = 180° 

100° + ∠B + 40° = 180° 

∠B = 180° - 140° = 40° 

Hence, Option 3 is correct.