Calculate the price in cents per gram for each packet of apples. Identify the option that gives the best value for money. Explain why prices do not always increase proportionally as quantity increases.

Given: 1 kg = R25
Convert kilograms to grams: $1 \text{ kg} = 1000 \text{ g}$
Convert Rands to cents: $25 \text{ R} = 25 \times 100 \text{ cents} = 2500 \text{ cents}$
Price per gram for 1 kg packet:

Given: 2 kg = R40
Convert kilograms to grams: $2 \text{ kg} = 2000 \text{ g}$
Convert Rands to cents: $40 \text{ R} = 40 \times 100 \text{ cents} = 4000 \text{ cents}$
Price per gram for 2 kg packet:

Given: 5 kg = R100
Convert kilograms to grams: $5 \text{ kg} = 5000 \text{ g}$
Convert Rands to cents: $100 \text{ R} = 100 \times 100 \text{ cents} = 10000 \text{ cents}$
Price per gram for 5 kg packet:

• 1 kg packet: $\boxed{2.5 \text{ cents/g}}$
• 2 kg packet: $\boxed{2 \text{ cents/g}}$
• 5 kg packet: $\boxed{2 \text{ cents/g}}$

The best value for money is the option with the lowest price per gram. Both the 2 kg packet and the 5 kg packet offer the lowest price of 2 cents/g.
The options that give the best value for money are the $\boxed{\text{2 kg packet and the 5 kg packet}}$.

Prices do not always increase proportionally with quantity due to economies of scale and marketing strategies. Supermarkets often offer bulk discounts to encourage customers to buy larger quantities, which can reduce packaging, handling, and administrative costs per unit for the seller. This allows them to sell larger packets at a lower price per unit (e.g., per gram) while still maintaining profitability.