John has 21 paper bills consisting of $20, $50, $100. He has twice as many $50 bills as $20 bills and has a total amount of 1380. How many of each type of bill does John have?

x = number of $20 bills

2x = number of $50 bills {he has twice as many $50 bills as $20 bills}

21 - 3x = number of $100 bills {total number of bills minus $20 and $50 bills}

20x + 50(2x) + 100(21 - 3x) = 1380 {value of bill times number of bills equals total value}

20x + 100x + 2100 - 300x = 1380 {used distributive property}

-180x + 2100 = 1380 {combined like terms}

-180x = -720 {subtracted 2100 from each side}

x = 4 $20 bills {divided each side by -180}

2x = 8 $50 bills {substituted 4, in for x, into 2x}

21 - 3x = 9 $100 bills {substituted 4, in for x, into 21 - 3x}

**John has 4 - $20 bills, 8 - $50 bills, and 9 - $100 bills**

*- Algebra House*