Even though each pollen grain has 2 male gametes, why atleast 20 pollen grains are required to fertilize 20 ovules in a particular carpel?

While each pollen grain has two male gametes, at least 20 are needed for 20 ovules due to double fertilization. One gamete fuses with the egg, and the other with the central cell, requiring a 1:1 ratio of pollen to ovules. This ensures both fertilization and endosperm formation for embryo development.