In the decimal system of numeration the number of 6-digit numbers in which the digit in any place is greater than the digit to the left of it is
A.
210
B.
84
C.
126
D.
None of these
Answer :
84
Solution :
Any selection of six digits from 9 digits (excluding 0) will give a number of the required variety.
∴ the required number of numbers $$ = {\,^9}{C_6}.$$
Releted MCQ Question on Algebra >> Permutation and Combination
Releted Question 1
$$^n{C_{r - 1}} = 36,{\,^n}{C_r} = 84$$ and $$^n{C_{r + 1}} = 126,$$ then $$r$$ is:
Ten different letters of an alphabet are given. Words with five letters are formed from these given letters. Then the number of words which have at least one letter repeated are
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