Natalie has some pennies and some nickels. She has at least 18 coins worth at most $0.66 combined. If Natalie has 11 nickels, determine the maximum number of pennies that she could have.
If Natalie has 11 nickels, then the value of the nickels is 11*$0.05=$<<11*0.05=0.55>>0.55
The total value of the pennies and nickels combined is at most $0.66
Let's say she has P pennies.
Assuming all of Natalie's coins are pennies, the maximum amount of money they can be worth is P*$0.01=P*0.01
The value of the pennies and nickels combined is at most $0.66
P*0.01+0.55<=$0.66
Multiply through the inequality by 100:
100P+55<=66
Subtract 55 from both sides:
100P<=11
Divide both sides by 100:
P<=11/100
So, Natalie can have a maximum of 11/100=$<<11/100=0.11>>0.11 pennies. Answer: \boxed{0}.