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

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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) About Me  (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 x%2By=15 and solving for y gives you y=15-x


Because you know that the mass of the old pennies are 3.10g and new pennies are 2.50gm, this means that 3.1x%2B2.5y=T where T is the total weight of all the coins combined.


Now plug in y=15-x to get 3.1x%2B2.5%2815-x%29=T


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