Question 86838
Let x=number of $5 bills in Anna's wallet
Then 12-x=number of $10 bills in her wallet

Value of $5 bills=$5x
Value of $10 bills=$10(12-x)

Now we are told that the total value of the bills is $100.  So----


$5x+$10(12-x)=$100  get rid of parens

$5x+$120-$10x=$100  subtract $120 from both sides

$5x+$120-$120-$10x=$100-$120  collect like terms

-$5x=-$20  divide both sides by -$5

x=4---------------------number of $5 bills

12-x=12-4=8----------------------------number of $10 bills

CK

$5(4)+$10(8)=$100

$20+$80=$100

$100=$100


Hope this helps---ptaylor