Question 1118952
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Let P the number of pennies and N be the number of nickels in the jar.


Then the coins worth is  P + 5N  cents  and the equation is


P + 5N =  920     (1)     (cents)


Now, under the "if" scenario, it would be P nickels and N pennies, that would worth 5P + N  cents.  So, the second equation is


5P + N = 2680     (2)    (cents)


Thus you have this system of two equation in 2 unknowns


P + 5N =  920     (1) 
5P + N = 2680     (2)


To solve it, from eq(1) express  P = 920-5N, and then substitute it into eq(2), replacing P. You will get a single equation for only one unknown N:


5*(920-5N) + N = 2680.


Simplify and solve for N:


4600 - 25N + N = 2680.


-24N = 2680 - 4600


-24N = -1920  ====>  N = {{{(-1920)/(-24)}}} = 80.


Thus there are 80 nickels in the original collection.


Then the number of pennies is  P = 920 - 5N = 920 - 5*80 = 920 - 400 = 520.
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Solved.