Explanation

Step 1: Convert both weights to the same unit

1 kg = 1000 g

3½ kg = 3.5 kg = 3.5 × 1000 g = 3500 g

Step 2: Calculate the ratio

Ratio = 3500 g : 50 g

= 3500 / 50

= 70

Step 3: Express the ratio in the required format

The ratio is 70:1.