Which of the following tactics increases the growth of existing products in an existing market?

Choosing market penetration as the correct tactic for increasing the growth of existing products in an existing market is sound because it focuses on strategies designed to increase market share for products that are already available. This can be achieved through various means such as increasing promotional efforts, improving sales tactics, pricing strategies, or enhancing customer satisfaction to encourage repeat purchases.

Market penetration aims to attract more customers within the same market, thereby increasing sales volume without changing the product or entering new markets. For example, a company might offer discounts, increase advertising, or enhance distribution coverage to boost sales of a current product.

Meanwhile, the other options represent different strategic approaches that do not align specifically with the goal of growing existing products in an existing market. Diversification would involve entering new markets with new products, market development entails introducing existing products to new markets, and product portfolio expansion suggests adding new products to the range, rather than focusing on increasing sales of current products in the existing market. Therefore, market penetration is the most direct method to achieve growth in this scenario.