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Algebra

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13 Aug 2010 17:31:51 IST

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There are 12 Balls in a bag, One of the ball is defective, you do not know if it weighs more or less

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There are 12 Balls in a bag, One of the ball is defective, you do not know if it weighs more or less. Weighing them not more than 3 times you need to find the defective ball.

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utkarsh singh

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13 Aug 2010 18:28:42 IST

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devide balls in 3 groups of 4-4 each now weigh them (1 st time)nw one of the the groups will show different weigh than other two.now devide this group into 2 grups of 2-2 balls.u had already obtained the weight of 4 non-defective balls so devide it by 2 to obtain the weight of 2 non-defective balls.now weight the new 2-2 groups u have made(2 nd time)the pair of balls showing deviation from your calculated value is defective group.now take the two balls of this group seperately and weight them also calculate the weight of one ball by deviding ur earler calculated value by 2 and now weigh each one of these balls(3 rd time) u shall know which ball is defective.

edison

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16 Aug 2010 13:17:58 IST

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Its not correct !!!

Gaurav |spideyunlimited| Ragtah

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16 Aug 2010 20:07:41 IST

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This requires a slightly elaborate solution and good wording is key to comprehending the solution. The following has been taken from http://www.scientificpsychic.com/mind/balls1.html

Label the balls from 1 to 12 to identify them.
Weigh 1, 2, 3, 4 against 5, 6, 7, 8:

If they balance, 9, 10, 11, 12 contain the odd ball.
Weigh 6, 7, 8 against 9, 10, 11.
1. If they balance, 12 is the odd ball. Weigh 12 against any other ball to discover whether it is heavy or light.
2. If 9, 10, 11 are heavy, they contain an odd heavy ball. Weigh 9 against 10. If they balance, 11 is the odd heavy ball, otherwise the heavier of 9 and 10 is the odd ball.
3. If 9, 10, 11 are light, we use the same procedure to reach the same conclusion for the odd light ball.
If 5, 6, 7, 8 are heavy, either they contain an odd heavy ball or 1, 2, 3, 4 contain an odd light ball.
Weigh 1, 2, 5 against 3, 6, 10.
1. If they balance, the odd ball is 4 (light) or 7 or 8 (heavy). Weigh 7 against 8. If they balance 4 is light, otherwise the heavier of 7 and 8 is the odd heavy ball.
2. If 3, 6, 10 are heavy, the odd ball can be 6 (heavy) or 1 or 2 (light). Weigh 1 against 2. If they balance 6 is heavy, otherwise the lighter of 1 and 2 is the odd light ball.
3. If 3, 6, 10 are light, the odd ball is 3 and light or 5 and heavy. We thus weigh 3 against 10. If they balance, 5 is heavy, otherwise 3 is light.
If 5, 6, 7, 8 are light we use a similar procedure to that in II.

Hope, this was clear and sufficiently detailed.

varun kumar

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15 Nov 2010 19:52:14 IST

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earth gravity is 9.18 can u tell me how have they find this value..........?

Harsh Gurung

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9 Feb 2011 10:42:37 IST

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superb .

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