In math class, we learned some methods to solve practical problems. Let's apply these methods to help you decide which swimming card is more cost-effective.

First, we can calculate the average cost of each swim.

For the second card, the cost of a swim is 35 yuan, so the average cost of each swim is 35 yuan.

For the annual card, the price is 1989 yuan, but you can swim unlimited times throughout the year. Suppose you swim once a week, so there are 52 weeks in a year, then the average cost of each swim is 1989 yuan divided by 52 times, which is about 38.25 yuan.

Therefore, from the average cost point of view, the cost of each swimming of Erka is relatively low.

However, we also need to consider the actual use. If you only swim once a week, the annual card may not be cost-effective. However, if you plan to travel twice or more a week, the annual card may be more cost-effective, because you can travel more times in a year without extra cost.

Generally speaking, if you plan to swim often, then the annual card may be more cost-effective. But if you only plan to go swimming occasionally, then the second card is more cost-effective. I hope this solution can help you!