How many total numbers of seven-digit numbers can be formed having sum of whose digits is even is Pick one:
A) 9000000 B) 4500000 C) 8100000 D) 4400000 E) None of these
Suppose x1 x2 x3 x4 x5 x6 x7 represents a seven digit number. Then x1 takes the value 1, 2, 3, ....., 9 and x2, x3,....., x7 all take values 0, 1, 2, 3, ......, 9.   If we keep x1, x2, ......, x6 fixed, then the sum x1 + x2 + ......+ x6 is either even or odd. Since x7 takes 10 values 0, 1, 2, ....., 9, five of the numbers so formed will have sum of digits even and 5 have sum odd.   Hence the required number of numbers   = 9 . 10 . 10 . 10 . 10 . 10 . 5 = 4500000   Answer 4500000
<result>B</result>
How many total numbers of seven-digit numbers can be formed having sum of whose digits is even is