smc

When a student multiplied the number $66$ by the repeating decimal, $$\underline{1}.\underline{a}\underline{b}\underline{a}\underline{b}\dots =\underline{1}.\overline{\underline{a}\underline{b}},$$ where $a$ and $b$ are digits, he did not notice the notation and just multiplied $66$ times $\underline{1}.\underline{a}\underline{b}.$ Later he found that his answer is $0.5$ less than the correct answer. What is the $2$-digit number $\underline{a}\underline{b}?$