Number Properties + Average!!

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apoorva.srivastva: Master | Next Rank: 500 Posts; Posts: 146; Joined: Wed Aug 27, 2008 5:41 am; Thanked: 3 times

by apoorva.srivastva » Fri Feb 19, 2010 11:23 am

The Values of five numbers are either 10,20 or 30. What is the average of 5 numbers?

1.) 4 numbers are less than 30
2.) 2 numbers are greater than or equal to 20

please explain the reasoning!!

OA is C

Last edited by apoorva.srivastva on Fri Feb 19, 2010 11:59 am, edited 1 time in total.

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Source: Beat The GMAT — Data Sufficiency | Fri Feb 19, 2010 11:23 am

harsh.champ: Legendary Member; Posts: 1132; Joined: Mon Jul 20, 2009 3:38 amFollowed by: 6 members; Location: India; Thanked: 64 times; GMAT Score:760

by harsh.champ » Fri Feb 19, 2010 11:39 am

apoorva.srivastva wrote:The Values of five numbers are 10,20 or 30 repectively. What is the average of 5 numbers?

1.) 4 numbers are less than 30
2.) 2 numbers are greater than or equal to 20

please explain the reasoning!!

OA is C

Shouldnt it be values of three no.s are 10,20 and 30 rather than for 5 no.s
Also,it is written respectively but or is also written.
Is the question correctly written??
Can u plz check??

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apoorva.srivastva: Master | Next Rank: 500 Posts; Posts: 146; Joined: Wed Aug 27, 2008 5:41 am; Thanked: 3 times

by apoorva.srivastva » Fri Feb 19, 2010 12:00 pm

harsh.champ wrote:
apoorva.srivastva wrote:The Values of five numbers are 10,20 or 30 repectively. What is the average of 5 numbers?

1.) 4 numbers are less than 30
2.) 2 numbers are greater than or equal to 20

please explain the reasoning!!

OA is C
Shouldnt it be values of three no.s are 10,20 and 30 rather than for 5 no.s
Also,it is written respectively but or is also written.
Is the question correctly written??
Can u plz check??

I have edited the post ...but the question stem says 5 nos and not 3 nos!!
this is a bit tricly DS qustion

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harsh.champ: Legendary Member; Posts: 1132; Joined: Mon Jul 20, 2009 3:38 amFollowed by: 6 members; Location: India; Thanked: 64 times; GMAT Score:760

by harsh.champ » Fri Feb 19, 2010 12:10 pm

apoorva.srivastva wrote:The Values of five numbers are either 10,20 or 30. What is the average of 5 numbers?

1.) 4 numbers are less than 30
2.) 2 numbers are greater than or equal to 20

please explain the reasoning!!

OA is C

Okay,now its fine.
1:- 4 numbers are less than 30.
Hence,the 5th no. is 30.
But we dont know the values of the other 4 numbers.Hence insufficient.

2:-2 numbers are GT or ET 20 .Still,it is insufficient.

Taking both 1 & 2 together ,
4 numbers are less than 30.[Frm 1]
Hence,the 5th no. is 30.
Now,2 no.s are greater than or equal to 20 .[Frm 2]
So, from 1 and 2 we get that the 4th no. is 20.

So,we can deduce that the rest of the 3 no.s are 10.

Hence,average = (3 x 10 + 20 + 30)/5 = 80/5
Hence,C.

I hope the explanation is clear.

It takes time and effort to explain, so if my comment helped you please press Thanks button

Just because something is hard doesn't mean you shouldn't try,it means you should just try harder.

"Keep Walking" - Johnny Walker

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apoorva.srivastva: Master | Next Rank: 500 Posts; Posts: 146; Joined: Wed Aug 27, 2008 5:41 am; Thanked: 3 times

by apoorva.srivastva » Fri Feb 19, 2010 12:23 pm

yeh mate ur explanation is cool....your approach and my approach is the same!!

but i took around 5 mints to crack it :(

was trying to look for an alternate approach!! i guess this is the best way to approach it :)

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shashank.ism: Legendary Member; Posts: 1022; Joined: Mon Jul 20, 2009 11:49 pmFollowed by: 2 members; Location: Gandhinagar; Thanked: 41 times

by shashank.ism » Sun Feb 21, 2010 6:14 am

apoorva.srivastva wrote:The Values of five numbers are either 10,20 or 30. What is the average of 5 numbers?

1.) 4 numbers are less than 30
2.) 2 numbers are greater than or equal to 20

please explain the reasoning!!

OA is C

Values of five numbers are either 10,20 or 30... so 2 numbers or more are equal..
St.1) 4 nos. are less than 30 hence one no. is 30 and other numbers could be (10,10,10,10),(20,20,20,20),(10,20,20,20)==========not suff..
St.2) 2 numbers are greater than or equal to 20. so so numbers may be (20 ,20), (30,30), (20,30)==========not suff..
Combined:
numbers are 20,30,10,10,10
av. of numbers = (20+30+10+10+10)/5 = 16 suff...Ans C

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