There is a number of three digits, 1 is never immediate right of 2 is? (A)771 (B) 791 (C) 881 (D)891. I faced this Question in Aptitude Competitive exam and don't know what the question actually means. Please anyone help me answering this question.
There is a number of three digits, 1 is never immediate right of 2 is?
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number-theory
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1The language sounds off, but if you want a guess I think it means that the block $21$ never occurs. (I think "intermediate" should be "immediate"). – 2017-02-05
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0Hint: assuming that my reading is correct (not certain) then it is easier to count the three digit numbers in which the block $21$ does occur. – 2017-02-05
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0oh sorry I am Editting it again yes You are right sir – 2017-02-05
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0The question should be: "What is the amount of $3$-digit numbers not containing the sequence '21'?". – 2017-02-05
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0And the answer is $900-10-9=881$. – 2017-02-05
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0can you explain your answer please? – 2017-02-05
1 Answers
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We have total 900 three digit numbers from 100-999.
I think its typo it should be immediate.
We have numbers in which 1 is immediate right to 2 are 210-219, 121, 221, 321, 421, 521, 621, 721, 821, 921.
So we have numbers in which 1 is never immediate right of 2 = 900 - 19 = 881 numbers.
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0thank you so much sir..thank you..yes it is right – 2017-02-05
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0Mine pleasure :-) – 2017-02-05