The amounts remaining for the first card form is 1/3 and for the second one is 1/10th. To resolve these two fractions to a common denominator, multipy the denominators together to get 30 and then multiply the numerator of the 1/3 by 10 = 10/30 and for the 1/10 muliply the denominator by 3 to get 30 and then the numerator by 3 to get 3/10 so the total is 13/30 left.
