The answer is the last one; to express very large or small numbers.
We use it so we can show big or very small numbers in an easier way.
Two thirds.
1/3 +1/3 = 2/3.
You don’t add the denominator (bottom terms), you only add the numerators (the top terms)
MP is the best choice as both triangles have MP as the same vector
Then the probability is
P(a)+P(b)-P(a&b)
0.5+0.3-0.5*0.3=0.8-0.15=0.65