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6.Permutation and Combination
medium
Six ‘$+$’ and four ‘$-$’ signs are to placed in a straight line so that no two ‘$-$’ signs come together, then the total number of ways are
A
$15$
B
$18$
C
$35$
D
$42$
(IIT-1988)
Solution
(c) The arrangement can be make as $.+.+.+.+.+.+.$, the $( – )$ signs can be put in $7$ vacant (pointed) place.
Hence required number of ways ${ = ^7}{C_4} = 35$.
Standard 11
Mathematics