Thief and diamonds

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

Thief and diamonds

by harsh.champ » Thu Feb 04, 2010 2:16 pm

A thief was stealing diamonds from a jewellery store. On his way out, he encountered three guards, each was given half of the existing diamonds and two over it by the thief. In the end, he was left with one diamond. How many did the thief steal?

(1)40
(2)36
(3)32
(4)28
(5)26

___________
Hey Stuart and Ian,
I solved this equation by taking no. of diamonds initially= x and solving the corresponding equations.
Is there any shortcut method of solving these type of questions because the above method took some time??

Quote

Source: Beat The GMAT — Problem Solving | Thu Feb 04, 2010 2:16 pm

ajith: Legendary Member; Posts: 1275; Joined: Thu Sep 21, 2006 11:13 pm; Location: Arabian Sea; Thanked: 125 times; Followed by:2 members

by ajith » Thu Feb 04, 2010 3:12 pm

harsh.champ wrote:A thief was stealing diamonds from a jewellery store. On his way out, he encountered three guards, each was given half of the existing diamonds and two over it by the thief. In the end, he was left with one diamond. How many did the thief steal?

(1)40
(2)36
(3)32
(4)28
(5)26

___________
Hey Stuart and Ian,
I solved this equation by taking no. of diamonds initially= x and solving the corresponding equations.
Is there any shortcut method of solving these type of questions because the above method took some time??

Well you can start by 1 diamond left in the end add 2 to get 3; double it 6; add two 8; double it 16; add 2 18; double it to get 36; which may be faster

Always borrow money from a pessimist, he doesn't expect to be paid back.

Quote

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

by harsh.champ » Thu Feb 04, 2010 3:17 pm

ajith wrote:
harsh.champ wrote:A thief was stealing diamonds from a jewellery store. On his way out, he encountered three guards, each was given half of the existing diamonds and two over it by the thief. In the end, he was left with one diamond. How many did the thief steal?

(1)40
(2)36
(3)32
(4)28
(5)26

___________
Hey Stuart and Ian,
I solved this equation by taking no. of diamonds initially= x and solving the corresponding equations.
Is there any shortcut method of solving these type of questions because the above method took some time??
Well you can start by 1 diamond left in the end add 2 to get 3; double it 6; add two 8; double it 16; add 2 18; double it to get 36; which may be faster

____________________
Thanks ajith,
Got the shortcut technique.Solving by the 1st method ,it took me around 3-4 minutes but when I applied your approach,I got the answer within 45 seconds.Way to go!!That means I save time for 1 additional question.Also,is it not advisable to approach the questions with the conventional "considering x" technique??
Thanks again.

Quote

ajith: Legendary Member; Posts: 1275; Joined: Thu Sep 21, 2006 11:13 pm; Location: Arabian Sea; Thanked: 125 times; Followed by:2 members

by ajith » Thu Feb 04, 2010 3:23 pm

harsh.champ wrote: ____________________
Thanks ajith,
Got the shortcut technique.Solving by the 1st method ,it took me around 3-4 minutes but when I applied your approach,I got the answer within 45 seconds.Way to go!!That means I save time for 1 additional question.Also,is it not advisable to approach the questions with the conventional "considering x" technique??
Thanks again.

I would say, whatever methods work for you do that. I wouldn't recommend wasting your time on inventing unconventional methods on a test day when you have a fool proof method. Having said that, if you have the shortcut ready and you have the confidence to apply it; why not?

See these are questions you need to find an answer to suit your style.

Always borrow money from a pessimist, he doesn't expect to be paid back.