There are 10,000 pennies in 100 dollars.
For every 1 dollar there are 100 pennies to every dollar so to find out how many pennies there are in 100 dollars you would take 100 pennies and multiply those 100 pennies by 100 to find out how many pennies are in 100 dollars.
So if we take 100 pennies and multiply it by another 100 we would get 10,000 so there are 10,000 pennies in 100 dollars.