Why do fish and frog produce a huge number of eggs each year?

Why do fish and frog lay more number of eggs whereas cow and human beings usually give birth to only one at a time?

Why do plants produce a large number of seeds?

Why do they differ from each other ?

Two progressive waves y_(1) = 4 sin 400 pi t and y_(2) = 3 Sin 404 pi t moving in the same direction superpose on each other producing beats. Then the number of beats per second and the ratio of maximum to minimum intensity of the resultant waves are respectively

Why do we produce more rice?

Why do the transition metals forin a large number of complex compounds ?