a simple way to do away with denominators, is we can simply multiply both sides by the LCD, in this case the LCD is 3, so let's multiply both sides by 3.

Rhombus -> 2 equivalent obtuse angles, 2 equivalent acute angles
vs.
Rectangle -> 4 equivalent right angles.
say, you have half a pie, and 2 sisters, if you divide the half-pie in 3 equal pieces, how much is everyone getting of the whole pie? well, is the quotient of 1/2 and 3.

The probability of Event A is 5/10 which simplifies to 1/2.
The probability of Event B is 3/9 which simplifies to 1/3.
Because it says "and" we need to multiply them which gives us 1/2*1/3=1/6