1 votes 1 votes In a multiple-choice test there are 6 questions. 4 alternatives answers are given for each question by choosing one answer for each question, then the number of ways to get exactly 4 correct answers is (A) ; (B) 135; (C) 9; (D) 120. Combinatory combinatory + – . asked Feb 23, 2017 • retagged Jun 27, 2017 by Arjun . 1.4k views answer comment Share Follow See 1 comment See all 1 1 comment reply Hemant Parihar commented Feb 23, 2017 reply Follow Share 135. First choose those 4 correct which are correct among the 6 question. So there are 6C4 = 15 ways. Now a correct can be choose only by clicking the correct option. So for an answer to be correct there is only one way. But for an answer to be wrong there are 3 ways. Suppose you got a sequence like this: CCCWCW. C is representing correct and W is representing wrong. So for this sequence we have 9 ways. 1*1*1*3*1*3 = 9. And there are 15 such sequences. So 15 * 9 = 135. 3 votes 3 votes Please log in or register to add a comment.
1 votes 1 votes answer is b 6C4*1*3*3= 135 arch answered Feb 23, 2017 arch comment Share Follow See all 0 reply Please log in or register to add a comment.