csat-suneung 2005 Q14

csat-suneung · South-Korea · csat__math-science 4 marks Combinations & Selection Counting Arrangements with Run or Pattern Constraints

Among 12-character strings made using all eight $a$'s and four $b$'s, how many strings satisfy all of the following conditions? [4 points] (가) $b$ cannot appear consecutively. (나) If the first character is $b$, then the last character is $a$.
(1) 70
(2) 105
(3) 140
(4) 175
(5) 210

Among 12-character strings made using all eight $a$'s and four $b$'s, how many strings satisfy all of the following conditions? [4 points]\\
(가) $b$ cannot appear consecutively.\\
(나) If the first character is $b$, then the last character is $a$.\\
(1) 70\\
(2) 105\\
(3) 140\\
(4) 175\\
(5) 210

Paper Questions

Q1 Q2 Q3 Q5 Q6 Q7 Q8 Q9 Q10 Q11 Q12 Q13 Q14 Q15 Q16 Q17 Q18 Q19 Q20 Q21 Q22 Q23 Q24 Q25 Q26 (Discrete Mathematics) Q26 (Probability and Statistics) Q27 (Discrete Mathematics) Q27 (Probability and Statistics) Q28 (Discrete Mathematics) Q28 (Probability and Statistics) Q29 (Discrete Mathematics) Q29 (Probability and Statistics) Q30 (Calculus and Differentiation) Q30 (Discrete Mathematics) Q30 (Probability and Statistics)