# 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

• 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...