SOLUTION: I am trying to figure out the number of old pennies and new pennies in a film jar (i have 15 pennies total). I know my mass of the pennies and old pennies are 3.10g and new pennie

Question 507064: I am trying to figure out the number of old pennies and new pennies in a film jar (i have 15 pennies total). I know my mass of the pennies and old pennies are 3.10g and new pennies are 2.50gm. please help with equation to figure out.

Answer by jim_thompson5910(35256) (Show Source): You can put this solution on YOUR website!
Let x = number of old pennies, y = number of new pennies

Since you "have 15 pennies total", this means that and solving for y gives you

Because you know that the mass of the old pennies are 3.10g and new pennies are 2.50gm, this means that where T is the total weight of all the coins combined.

Now plug in to get

Now if you knew the total weight T, then you could solve for x to find the number of old pennies in the jar.
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