[FredZarguna]

 32 = 10 0000B
 12 = 00 1100B
-12 = 11 0011B + 1 = 11 0100B

 32 - 12 = 32 + (-12) = 
 10 0000B
+11 0100B
_____________________
 01 0100B 
= 20. 

Hope this helps.

[FredZarguna]

Consider the intervals: A = (-∞, 12] and B = (-∞, 32] both intervals are ∈ ℬ and thus Lebesgue measurable.

The characteristic function χ_A vanishes identically on (12, +∞) while the characteristic function χ_B has support only (-∞, 32]. Both functions are measurable, so their difference χ_B - χ_A is measurable.

Thus: ∫ χ_B - χ_A = ∫ χ_B - ∫ χ_A = 20.

Hope this helps more clearly illustrate the concepts of basic subtraction for small children.