Since 1/3 are pennies, your number of coins is divisible by 3.
And since you have an even number of coins, your number of coins is divisible by 6.


So you could have 2 pennies, 3 dimes, and 1 other coin, say a nickel.

You'd have an even number of coins, 6.  One third of them, or 2, would be
pennies, and half of them, or 3, would be dimes.    


But you could multiply all these numbers by any whole number, and the same
would be true.
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You could have 2n pennies, 3n dimes, and n other coins, say nickels.

You'd have an even number of coins, 6n.  One third of them, or 2n, would be
pennies, and half of them or 3n would be dimes.

Edwin