Finding a Remainder when Dividing by 11

To find the remainder when dividing by 11, you use an alternating sum of the digits. Starting with the ones digit, you add and subtract the digits in sequence.

For 13542, the calculation is $2 - 4 + 5 - 3 + 1 = 1$. The remainder is 1.

An alternative is to sum the alternating digits separately and then subtract the sums. For 13542, this would be $(2+5+1) - (4+3) = 8 - 7 = 1$. Choose whichever method is faster for you.