# In 80 coins one coin is counterfiet what is minimum number of weighings to find out counterfiet coin?

This question is related to TCS Interview

Himanshu Ashwani Profile Answers by Himanshu Ashwani Questions by Himanshu Ashwani

• Member Since Oct-2008 | Oct 16th, 2008

Divide Coins As 27 27 26
now weigh 27 and 27 keeping on both sides of pan u will get the less one
and if both sides are equal then group that has 26 coins has the coin that is counterfiet...
if u get 27 as result divide it in 3 groups
9 9 9
and weight it
keep two groups on two sides of pans and get the result of both sides are equal then the group 9 which was not kept on the pan has the coin which is counterfiet....
now 9 is divided as in 3 groups as
3 3 3 and weigh again and get result
now divide 3 as
1 1 1 and get the coin..
in start if u get answer as 26 divide as 3 groups
9 9 8
wiegh by keeping 9 on both sides and get answer if both are equal then 8 is ans
if 9 is ans again divide as 3 3 3 and then 1 1 1 and get coin...
if u get 8 then divide as 2 2 2 then 1 1 less one be yours coin...

#### nigamleos Profile Answers by nigamleos

• Jan 31st, 2008

Ans. 5
as minimum is told. otherwise total 6.

#### avin2v2 Profile Answers by avin2v2

• Jul 23rd, 2008

3
since in 2 coins only 1 weighing is required
3            also 1    if  2 coins r identical then third coin is defective  or else  one  of the 2 is defective
4,5,6,7,8          needs  1  test
9 requires  2 tests
27 requires 3 tests
81 requires 4 tests
since 80 coins r used only 3 tests r enough

#### Himanshu Ashwani Profile Answers by Himanshu Ashwani

• Oct 16th, 2008

Divide Coins As 27 27 26
now weigh 27 and 27 keeping on both sides of pan u will get the less one
and if both sides are equal then group that has 26 coins has the coin that is counterfiet...
if u get 27 as result divide it in 3 groups
9 9 9
and weight it
keep two groups on two sides of pans and get the result of both sides are equal then the group 9 which was not kept on the pan has the coin which is counterfiet....
now 9 is divided as in 3 groups as
3 3 3 and weigh again and get result
now divide 3 as
1 1 1 and get the coin..
in start if u get answer as 26 divide as 3 groups
9 9 8
wiegh by keeping 9 on both sides and get answer if both are equal then 8 is ans
if 9 is ans again divide as 3 3 3 and then 1 1 1 and get coin...
if u get 8 then divide as 2 2 2 then 1 1 less one be yours coin...

#### Aarthyanbu Profile Answers by Aarthyanbu

• Dec 10th, 2009

It is about 5 times... First step to split those 80 coins into 40. then again split 40 to 20. divide 20 into 10 and then 5 finally 2 at last find the minimum weight...  