how many two - digit numbers yield a remainder of 1 when divided by both 6 and 15 ?
"easier to start with numbers that are of the form 15 p + 1 - - - > 16,31 , 46,61 , 76,91 . out of these 2 ( 31,61 ) are also of the form 6 q + 1 . thus 2 is the answer . c is the correct answer ."
subtract(add(1, multiply(15, 6)), multiply(15, 6))