Sally has twice as many dimes as nickels. The total value is $3.50. How many nickels does she have?

Question

Sally has twice as many dimes as nickels. The total value is $3.50. How many nickels does she have?

 

Show your calculation as an equation.

Answer 1

 

Let d = number of dimes

Let n = number of nickels

 

   10d + 5n = 350  (1)       ( expressing values in pennies )

 

There are two unknowns, so we need a 2nd equation.  The 2nd equation comes from "twice as many dimes as nickels":

 

      d = 2n    (2)

 

Substitute  "2n" for "d" in (1):    10(2n) + 5n = 350

                                                20n + 5n = 350

                                                     25n = 350

                                                        n = 14   

                                                        d = 2n = 2*14 = 28

 

                    14 nickels

                    28 dimes

 

(Always) check:    28*10 + 14*5 = 280 + 70 = 350  (checks out)