Marianna has only nickels and quarters in her piggy bank. their combined value is $9.15. their combined weight is one pound. ninety nickels weigh one pound. eighty quarters weigh one pound. how many nickels does marianna have in her piggy bank?

There are 63 nickels that Marianna have in her piggy bank.

Step-by-step explanation:

Let us assume that there are x nickels and y quarters in the bank.

Therefore, 0.05x + 0.25y = 9.15 ...... (1)

⇒ x + 5y = 183 ........ (2) {Multiplying both sides with 20}

Now, 90 nickels weighs 1 pound.

Then, x nickels weighs pounds

Again, 80 quarters weighs 1 pound .

Then, y quarters weighs pounds.

Given that, ........ (3)

⇒ x + 1.125y = 90 ......... (4) {Multiplying both sides with 90}

Now, subtracting equation (4) from equation (2) we get,

3.875y = 93

⇒ y = 24.

Now, from equation (4) we get, x = 90 - 1.125 (24) = 63.

So, there are 63 nickels that Marianna has in her piggy bank. (Answer)