Question

Anthony has a cup full of nickels and dimes worth $13.90. There are 196 coins all together.

Answer 1

The nickles and dimes are worth 13.90 
Since nickles are worth 5 cents and dimes worth 10 cents, we'll take the number of nickles, x and multiply by 5, and likewise the number of dimes, y and multiply by 10. Since we are using cents, we'll convert 13.90 to cents by moving the decimal two places.and making it 1390 

5x + 10y = 1390 

There are 196 coins. 
When counting them we'll just take the number of nickles, x, and add them to the number of dimes, y. 

x+y=196