The average of six number is 30.

Oldest

Best Reply

Author

Message

TAGS:

Intern

Joined: 04 Aug 2010

Posts: 14

Followers: 0

Kudos [?]: 0 [0], given: 12

The average of six number is 30. [#permalink]

15 Dec 2011, 08:55

00:00

Question Stats:

16% (01:26) correct

83% (01:08) wrong

based on 2 sessions

The average of six numbers is 30. If the average of first four is 25 and that of last three is 35, the fourth number is?

a) 25 b) 30 c) 35 d) 40

(Please include detailed solving process)

[Reveal] Spoiler: OA

Senior Manager

Joined: 11 May 2011

Posts: 383

Location: US

Followers: 1

Kudos [?]: 46 [1] , given: 46

Re: The average of six number is 30. [#permalink]

15 Dec 2011, 09:12

This post received
KUDOS

newmoon wrote:

The average of six numbers is 30. If the average of first four is 25 and that of last three is 35, the fourth number is?

a) 25 b) 30 c) 35 d) 40

(Please include detailed solving process)

My answer is A. Here is the explanation -
The average of first four is 25 => total = 25*4 = 100
The average of last three is 35 => total = 35*3 = 105
The average of six is 30 => total = 30*6 = 180

So we can form an equation - assuming fourth number = x
100+105-x = 180
Hence x = 25.

Cheers!
_________________

-----------------------------------------------------------------------------------------
What you do TODAY is important because you're exchanging a day of your life for it!
-----------------------------------------------------------------------------------------

Intern

Joined: 04 Aug 2010

Posts: 14

Followers: 0

Kudos [?]: 0 [0], given: 12

Re: The average of six number is 30. [#permalink]

15 Dec 2011, 09:20

Thanks Capricorn369. I get A too. The answer provided may be is wrong. Lets see what other people come up with.

Magoosh Co-Founder

Joined: 17 Sep 2011

Posts: 38

Schools: UC Berkeley (Haas) - Class of 2010

Followers: 12

Kudos [?]: 14 [1] , given: 10

Re: The average of six number is 30. [#permalink]

15 Dec 2011, 09:22

This post received
KUDOS

Hi @newmoon,

What's the source of this question? I first noticed that, unlike a typical GMAT question, this question only has 4 answer choices. Also, the question does not specify the order of the numbers, so finding the fourth number could be ambiguous. Lastly, I get an answer different than the OA.

If we assume the 4th number is the one that exists in both sets, then we could solve the question as follows
1. The first four numbers have an average of 25, therefore their sum must be 100 (because 100/4 = 25)
2. The last three numbers have an average of 35, therefore their sum must be 105
3. All six numbers have an average of 30, therefore their sum must be 180

Let's call our six numbers: A, B, C, D, E, F, G
A + B + C + D = 100
D + E + F = 105
A + B + C + D + E + F = 180

using substitution we get:
100 + 105 - D = 180 (we have to subtract D because it was in both sets)
205 - D = 180
D = 25
_________________

Bhavin Parikh
Magoosh Test Prep

Intern

Joined: 06 Nov 2011

Posts: 3

Location: Peru

GPA: 3

Followers: 0

Kudos [?]: 5 [0], given: 0

Re: The average of six number is 30. [#permalink]

15 Dec 2011, 10:00

I've just re-read the question and it is true, answer is not 35, as I thought, I'm ediding to avoid confussion. Regards!!

Last edited by cuet16 on 15 Dec 2011, 15:11, edited 1 time in total.

Intern

Joined: 21 Nov 2011

Posts: 2

Followers: 0

Kudos [?]: 3 [2] , given: 1

Re: The average of six number is 30. [#permalink]

15 Dec 2011, 10:13

This post received
KUDOS

Lets say numbers are n1, n2, n3, n4, n5, n6

Average of six numbers is 30. n1+n2+n3+n4+n5+n6 = 30*6 = 180
Average of first four is 25. n1+n2+n3+n4 = 25*4 = 100

From the above two statements, n5+n6 = 80

Average of last three is 35. n4+n5+n6 = 35*3 = 105

So n4 = 105 - 80 =25

Manager

Joined: 31 Oct 2011

Posts: 52

Location: India

Followers: 0

Kudos [?]: 13 [0], given: 11

Re: The average of six number is 30. [#permalink]

15 Dec 2011, 11:18

6 numbers = a,b,c,d,e,f,

(a+b+c+d+e+f/6)=30

a+b+c+d+e+f=180

(a+b+c+d)/4=25

So,
(a+b+c+d)=100

(d+e+f)/3=35

So, d+e+f=105

so the fourth number(d) is :{[(a+b+c+d)+(d+e+f)]-(a+b+c+d+e+f)} = d = (100+105)-180
i.e 25

The answer given as 35 is def wrong.Change it to A (25)
_________________

Regards,
Rajesh
Helping hands are anytime better than praying hearts

Kudos ???!@#$$ !!! I just love them

Re: The average of six number is 30. [#permalink] 15 Dec 2011, 11:18

		Similar topics	Author	Replies	Last post
Similar Topics:		If the average (arithmetic mean) of six numbers is 75, how	shahnandan	6	27 Jan 2006, 01:49
		15 numbers between 20 and 30 (inclusive?), is their average	getzgetzu	2	06 May 2006, 04:49
		If the average (arthmetic means) of six numbers is 75, how	faifai0714	2	01 Mar 2007, 01:05
	1	For a lottery ticket, Emily chose six numbers that average	badgerboy	4	17 Oct 2009, 05:44
	2	If the average (arithmetic mean) of six numbers is 75, how	GMATD11	4	21 Feb 2011, 09:40

The average of six number is 30.

Main navigation

GMAT Resources

Partners

MBA Resources

GMAT ® is a registered trademark of the Graduate Management Admission Council ® (GMAC ®). GMAT Club's website has not been reviewed or endorsed by GMAC.

GMAT Courses

Admissions Consulting

The average of six number is 30.

The average of six number is 30.

Main navigation

GMAT Resources

Partners

MBA Resources