13. China's high-speed rail development is rapid and technologically advanced. According to statistics, among high-speed trains stopping at a certain station, 10 trains have an on-time rate of 0.97, 20 trains have an on-time rate of 0.98, and 10 trains have an on-time rate of 0.99. The estimated value of the average on-time rate for all high-speed trains stopping at this station is $\_\_\_\_$ .