Let

x = number of nickles

y = number of quarters

1 nickle = 5 cents

1 quarter = 25 cents

There are 20 more nickels than quarters:

x = y + 20

The value of the nickels equals the value of the quarters:

5x = 25y

We have the following system of equations:

x = y + 20

5x = 25y

........

click here to see the system of equations solved for x and y

........

x = 25 nickles

y = 5 quarters

There are 5 quarters in the jar.