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505-555 (Easy)|   Algebra|      
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What is the average (arithmetic mean) of 3x and 15z? (1) x + 5z = 20 Updated on: 13 Apr 2020, 01:01
Originally posted by unraveled on 12 Apr 2020, 00:49.
Last edited by unraveled on 13 Apr 2020, 01:01, edited 1 time in total.
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Question Stats:

77% (00:47) correct 23% (00:48) wrong based on 118 sessions

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What is the average (arithmetic mean) of 3x and 15z?

(1) x + 5z = 20
(2) x + z = 8
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A
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What is the average (arithmetic mean) of 3x and 15z? (1) x + 5z = 20 12 Apr 2020, 02:56
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lnm87
What is the average (arithmetic mean) of 3x and 15z?

(1) x + 5z = 20
(2) x + z = 8
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Never fall for C trap, and for that simplify the question and see if any statement helps you.

We are looking for average if 3x and 15z that is \(\frac{3x+15z}{2}=\frac{3(x+5z)}{2}\)

I. x+5z=20..
So average = 3*20/2=30

II. x+z=3..
We require another equation

A
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What is the average (arithmetic mean) of 3x and 15z? (1) x + 5z = 20 12 Apr 2020, 03:07
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lnm87
What is the average (arithmetic mean) of 3x and 15z?

(1) x + 5z = 20
(2) x + z = 8

Never fall for C trap, and for that simplify the question and see if any statement helps you.

We are looking for average if 3x and 15z that is \(\frac{3x+15z}{2}=\frac{3(x+5z)}{2}\)

I. x+5z=20..
So average = 3*20/2=30

II. x+z=3..
We require another equation

A
Show more
I fell for C-trap. Also, i could not understand what it asked. I thought it was about statements giving values of x and z but it was not. So, more than knowing that it was about 3x and 5z as two entities i took it as x and z are variable the values of which should be available for solving the question.

Anyway learnings in hard manner. :|
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What is the average (arithmetic mean) of 3x and 15z? (1) x + 5z = 20 12 Apr 2020, 05:12
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(1) x + 5z = 20
or,3(x+5z)=60
or, (3x+15z)/2=30
so,the average (arithmetic mean) of 3x and 15z = 30 sufficient

(2)x + z = 8
can't find average (arithmetic mean) of 3x and 15z insufficient

correct answer A
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What is the average (arithmetic mean) of 3x and 15z? (1) x + 5z = 20 12 Apr 2020, 08:27
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What is the average (arithmetic mean) of 3x and 15z?

(1) x + 5z = 20
(2) x + z = 8

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Question is 3x+15z / 2 = ?

So we need to find out values for two variables x and z.
(1) multiple by 3. LHS, we have 3x + 15z and RHS we have 60.
This gives the sum for 3x + 15z. sufficient.

(2) insufficient.

IMO, the answer is A.
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What is the average (arithmetic mean) of 3x and 15z? (1) x + 5z = 20 12 Apr 2020, 09:36
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What is the average (arithmetic mean) of 3x and 15z?

(1) x + 5z = 20
(2) x + z = 8

Arithmetic mean of 3x and 15z is (3x+15z)/2 or if we know the value of 3x+15z, we are through.

Statement 1: x + 5z = 20. Multiply this by 3, we get - 3x + 15z = 60. We are done. Arithmetic of 3x and 15z is 60/2 = 30. Statement 1 is sufficient.

Statement 2: x + z = 8. We have multiple values of x and z, for x = 1, 1 + z = 8 or z = 7, Arithmetic mean of 3x and 15z will be (3 +105)/2 = 108/2 = 54
If x = 4 and z = 4, arithmetic mean of 3x and 15z will be (12 + 60)/2 = 72/2 = 24.

So, statement 2 is not sufficient.

Answer choice A. Statement 1 alone is sufficient but 2 is not sufficient.
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What is the average (arithmetic mean) of 3x and 15z? (1) x + 5z = 20 27 Jul 2021, 23:43
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