Question

The sum of the digits at the 10th place of all numbers formed with the help of 2, 4, 5, 7 taken all at a time is .....

(a) 432 

(b) 108 

(c) 36 

(d) 18

Answer 1

(b) 108

Number of digits given = 2, 4, 5, 7 

Number of 4 digit numbers formed = 4! = 24 

So each digit occur 24/4 = 6 times 

Sum of the digits = 2 + 4 + 5 + 7 = 18 

So sum of the digits in each place = 18 × 6 = 108