money

 

Thirty coins, all dimes and nickels, are worth $2.60. How many nickels are there?   

 

IF all 30 coins were dimes, you'd have $3.00. 

You have only $2.60, therefore you need to reduce the total by 40¢. 

Every time you substitute a nickel in place of a dime, you lose 5¢. 

So, you need to replace 8 dimes with nickels to lose 40¢.  

That makes a final mix of 22 dimes and 8 nickels.  

So the answer to the question is 8 nickels.  

 

Check:     22 dimes    =  $2.20  

                  8 nickels   =  $0.40  

                                     ––––––

Total                               $2.60  

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Let the number of nickels = N

The number of dimes        =30 - N

 

0.05N  +  0.10*[30 - N] = 2.60, solve for N

N =8 nikels

30 - 8 nickels =22 dimes.