GMAT OFFICIAL GUIDE PS

Solution:

We are given that the operation ⊙ is defined by x⊙y = √(xy) for all positive numbers.

We are next given that (5⊙45)⊙60. Following PEMDAS rules, we want to begin with the operation inside the parentheses. According to the operation, x will be replaced with 5, and y will be replaced with 45. Thus, we have:

5⊙45 = √(5*45) = √225 = 15

We have determined that (5⊙45) = 15, so we substitute 15 for (5⊙45) to obtain 15⊙60.

According to the operation, x will now be replaced with 15 and y will now be replaced with 60. Thus we have:

15⊙60 = √(15*60) = √900 = 30

Answer: A

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Scott Woodbury-Stewart is the founder & CEO of Target Test Prep. A passionate teacher who is deeply invested in the success of his students, Scott began his career teaching physics, chemistry, math, and biology. Since then, he has spent more than a decade helping students gain entry into the world’s top business schools, logging 10,000+ hours of GMAT, EA, GRE and SAT instruction. Scott also served as lead content developer and curriculum architect for the revolutionary courses Target Test Prep GMAT, Target Test Prep EA, Target Test Prep GRE and Target Test Prep SAT Quant.