Question

Why do fish and frogs lay eggs in the hundreds?

Answer 1

Just because the life of their eggs are not sure. They can be damaged, die and destroyed by so for getting some child from eggs they lay so many eggs so that if some of them will die also then some will be alive

Answer 2

They lay so many eggs because these organisms live in water ....and they practice external fertilisation....all the eggs they lay do not fertilise because these gametes get exposed to the water currents,wind,rainfall and predators in the water....all these factors prevent the contact between the 2 gametes....therefore to sure that fertilisation takes place they produce so many eggs
Hope it helps ...✌✌