Find the missing bank digit:

2 ? 6 9 2 4 4 1 7

Calculate what you get from the numbers you know:

2*7+x*3+6*9+9*7+2*3+4*9+4*7+1*3+7*9=

4+x*3+4+3+6+6+8+3+3 = x*3+7

so in order to get 0 mod 10, I need x*3 to end in 3. 1*3=3, so the missing digit is 1