Even though each pollen grain has two male gametes, why are at least 10 pollen grains and not 5 pollen grains required to fertilise 10 ovules present in a particular carpel ?

Explanation

This is so because of occurrence of double fertilization. One of the male gametes fused with the egg cell and results in the formation of diploid zygote. The other male gamete fused with the central cell to produce a tripoid endosperm