In the decimal system of numeration of the number of 6-digit number in which the digit in any pace is greater than the digit to the left of it is (A)210 (B) 84 (C) 126 (D)none

CORRECT ANSWER IS 84

total number : 9*8*7*6*5*4 as we want one of the arrangement of a single selection in which the digits are arranged in particular order. Hence, if we divide the total ways by 6!, we will get the desired result hence ans is (9.8.7.6.5.4)/6! = 84