Digvijay01 wrote:Hi.. this is a Qs from Magoosh..
Can you tell.. how can we do the below Qs by plugging in no.s. I already know algebraic method.
The average (arithmetic mean) of y numbers is x. If 30 is added to the set of numbers, then the average will be x - 5. What is the value of y in terms of x ?
a. x/7-5
b. x/6-6
c. x/6-5
d. x/5-7
e. x/5-6
Plug in y=1 -- implying that the original set includes only ONE value -- and solve for x.
Original set:
Sum = (number)(average) = 1*x = x.
New set:
Here, there are 2 values: the original value and 30.
Since the new average = x-5, the sum of the 2 values = (number)(average) = 2(x-5) = 2x-10.
Since the new set includes 30, while the original set does not, the difference between the two sums is 30:
(2x - 10) - x = 30
x=40.
The question stem asks for the value of y=1.
Thus, the correct answer choice must yield a value of 1 when we plug in x=40.
Only
D works:
(x/5) - 7 = 40/5 - 7 = 1.
The correct answer is
D.
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