I think it's better to look at the option here and make a guess using trial and error:
So, as evident, we need to take one from Y and add to X, means Y is smaller. By adding 1 to X, X must become 75% of total and Y must become 25% of total. So this mean the difference between the 2 must be significant after adding 1 to X.
Keeping this in mind, let's test
19&4, so 19+1=20, 4-1=3, 20+3=23, so 19 was already higher than the req. 75%, rejected.
So, we need
lesser gap, let's test
19&7. 19+1=20 and 7-1=6. Total= 20+6 = 26, now let's check if the purpose is fulfilled, 75% of 26=19.5=20 (as no. of people cant be in decimal). Yes, condition fulfilled. Y will be automatically 25%.
Be careful in these kinds of trial and error as if you don't eliminate options smartly it will take a lot of time and wouldn't be worth solving at the cost of much time. GMAT695
The chair of the board of directors for a certain company is planning to call a meeting of the board to vote on a measure. Passing a measure requires at least 75% of the members of the board to vote for the measure. The chair has taken an informal poll of the board members, and exactly x members (including the chair) said they would vote for the measure, while the remaining y members said they would vote against it. The chair correctly determined that the measure would not pass if all members voted as they said they would, but the measure would pass if the chair could convince just one member who said she would vote against the measure to instead vote for the measure,
assuming all other members vote as they said they would.
Select a value for x and a value for y that are jointly consistent with the information provided. Make only two selections, one in each column.