Question

If 12 persons are seated in a row, the number of ways of
selecting 3 persons from them, so that no two of them are
seated next to each other is?
A) 85
B)100
C)120
D)240
E)none of these
​

Answer 1

total persons are 12

selecting from there 3

so your combination questions possiblity ¹²c3

12×11×10÷3×2×1

so 220

then you have 3 possiblity of questions

1st of all you have prohibited from question

it means you caculate mare than one of three are sit together

1st is 3 all together that ans is 10

2 nd any to who sit last two sides

left n right so two

ang third have 9 places so

9×2=18

and third last two are together but not last two sits

so 9 two sits besides for them and third once have 8 place

so 9×8=72

10+72+18 =100

so 220-120=120

thank you..i hope u understand..

its very tpugh questions n answer for understanding....