There are 4 letters and 4 envelopes. Total no. of methods in which 2 letters can be posted correct

M4maths Previous Puzzles

18 Feb 2010 Letters and envelopes

There are 4 letters and 4 envelopes. Total no. of methods in which 2 letters can be posted correctly and 2 wrongly.

OPtion

1) 4
2) 7
3) 8
4) 9
5) 10
6) 15
7) 1
8) 6
9) 12
10) 24

Solution

Total no. of methods for selecting 2 letters out of 4 which has to be posted correctly = 4*3/2*1 = 6
No. of methods in which remaining 2 letters are posted wrongly is 1 only.
Hence total methods = 6*1 = 6

Correct Option: 8 Best Solution (5)

Dr.Dipin Singh   14 years AGO

If A,B,C and D are 4 letters
and
1,2,3,4 are 4 envelopes, then

possible arrangements for 2 correct letters are

A and B in correct envelope.and C and D incorrect .......
A and C... correct
A and D...correct
B and C.. correct
B and D...correct

C and D ...correct.

so only 6 arrangements

Like? Yes (1) | No   

Pargat Pal Singh   14 years AGO

Combinations possible for correct envelopes ...ab,ac,ad,bc,bd,cd.... 6 combinations

Like? Yes (1) | No   

Arneet   14 years AGO

12,13,14,23,24,34 in correct envelopes are 6 possible arrangements for given case.

Like? Yes (1) | No   

Bankim   14 years AGO

When 2 letters are in correct envelope, only 2 letters can be in wrong envelopes.

So we check only possible arrangements for 2 correct envelopes.
1st and 2nd
1st and 3rd
1st and 4th
2nd and 3rd
2nd and 4th
3rd and 4 th

so only 6 combinations

Like? Yes (1) | No   

bhuwan adhikari   14 years AGO

no. of ways sellecting 2 letters=6
posting these two correctly the remaining 2 can be posted wrongly in 1 way
therefore total no. of ways=6

Like? Yes (1) | No