Scott Woodbury-Stewart

GMAT OFFICIAL GUIDE PS – If the operation ⊙ is defined by x⊙y = …

If the operation ⊙ is defined by x⊙y = …

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