Complex sentence: This is because a value of one multiplied by 89 (sum of weights) is 89, and 89 divided by 11 is 8 with remainder 1/11; thus 1 is the check digit.
Split into simpler sentences: This is because a value of one, multiplied against 89 (sum of weights), is still 89. And 89 divided by 11 is 8 with the remainder being the fraction "1 over 11," thus 1 is the check digit.