Question

From a pile of 100 pennies(P), 100 nickels(N), and 100 dimes(D), select 21 coins which have a total value of exactly $1.00. In your selection you must also use at least one coin of each type. How many coins of each of the three types(P, N, D) should be selected?

Answer 1

So, you need 10 penny, 4 nickles and 7 dimes
Lets, check it.
According to the question,
total coins = 21
7 + 4 + 10 = 21
21 = 21.........................................true
Now,
their value should equal $1.00 = 100 cents
Penny = 1 cent
nickle = 5 cent
dime = 10 cent,
So,
(10 *1) + (4 * 5) + (7 * 10) = 100
10 + 20 + 70 = 100
100 = 100......................................true

 
So, you need 10 penny, 4 nickle, and 7 dimes