Cost per banana = 3/12 = 0.25. Selling price = 0.35. Profit% = ((0.35-0.25)/0.25) × 100 = 40%

Let numbers be 4x and 7x. 7x - 4x = 21, so 3x = 21, x = 7. Larger number = 7×7 = 49

Let distance = d, normal time = t. d/5 = t+2 and d/6 = t-1. Solving: d = 60 km

Milk:Water = 3:2. If milk = 15, then 3x = 15, x = 5. Water = 2×5 = 10 liters

A = 5000(1 + 10/100)² = 5000 × 1.21 = 6050. CI = 6050 - 5000 = 1050

If discount is 20%, then customer pays 80%. 0.8x = 400, x = 500

(81 × 8) / (9 × 4) = 648/36 = 18

Work per day = 1/12 + 1/15 = (5+4)/60 = 9/60 = 3/20. Time = 20/3 = 6⅔ days

Profit = 1080 - 900 = 180. Profit% = (180/900) × 100 = 20%

2(1)² + 3(1) - 5 = 2 + 3 - 5 = 0. So x = 1 is a solution.