The correct answer to this question is 100.101. The binary system is numeric, and it writes numbers using only the digits 0 and 1. These two numbers are also known as a true and false state. In this system, a digit is as twice as much as a digit to the right of them.
Many people invented this system, but the credit goes to mathematician Gottfried Leibniz. He created the system in 1679. Since then, it has gone on to be used in computers and calculators. This type of question could be found on a math test, as well as SATs.