As with many GMAT questions, there are many ways to arrive at the answer to this question! I am adding my two cents as part of my new project to go through all of the Quant questions in the 2019
Official Guide and share my suggested "GMAT Timing Tips" for each one: that is, what could you notice or do to be able to answer each question more efficiently? For this question, my GMAT Timing Tips are:
Two-set Venn Diagrams: Draw out the Venn Diagram to quickly see how the numbers you are given relate to what you are asked to calculate. As many people have done on this thread, you can find that 24 parents volunteered only to supervise children.
Use smart variables to represent unknowns: I recommend using the variable R to represent the total number of parents who volunteered to bring refreshments, because that is what the question asks us to solve for. Then, using the Venn Diagram and the information in the question, write the equation R = 1.5(84 - 24 - R), and just solve for R.
I'm also planning to create video solutions demonstrating how to use my GMAT Timing Tips for each of
the Official Guide Quant questions. This will take a while, but I'll start with the those that I get requests for first. If you would me to create a video solution for this question, please go to the page that I have created for this question and vote for or share it:
Of the 84 parents who attended a meeting at a school, 35..You can also ask me to answer a question about this GMAT practice question by asking it in this thread, or by using the question form on the page above, and I'll address it in my video solution. Please let me know if you have any questions!
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Online GMAT tutor with a 780 GMAT score. Harvard graduate.
Please read and share my free
GMAT Timing Strategy Guide!