I would do piecewise addition like this: Girl A is 1/3 of Table A, which seats half of the students, so she is 1/3 * 1/2 = 1/6 of the total. Girl B is 1/3 of

I would do piecewise addition like this: Girl A is 1/3 of Table A, which seats half of the students, so she is 1/3 * 1/2 = 1/6 of the total. Girl B is 1/3 of Table A, which seats half of the students, so she is 1/3 * 1/2 = 1/6 of the total. So girls represent 1/6 + 1/6 = 2/6 of the total.