10 pennies
1) Considering that:
1 penny = 1 cent
1 nickel = 5 cents
1 dime= 10 cents
2) We can write out the following equation relating all that:

Note that we wrote 'c" for coins:
3) Thus we can write the following as our answer picking the number of pennies as 1c
1c = 1 * 10 = 10 pennies