a = 1/(2×9) × (7 + 11/10) + 1/(33 × 10) × (13/2 + 17/5)
a = 1/18 × (70 + 11)/10 + 1/330 × (13×5 + 17×2)/10
a = 1/18 × 81/10 + 1/330 × (65 + 34)/10
a = 9/10 + 1/330 × 99/10
a = 9/10 × ( 1 + 1/330 × 11) = 9/10 × (330 + 11)/330 = 9/10 × 341/330
a = 3/10 × 341/110 = 3/10 × 31/10 = 93/100
