Question 430866
Solution:Let x the number of $5 bills, then 30-x is the number of $2 bills

Since he spend $120 we write: {{{5x+2(30-x)=120}}}, solve the equation.

5x-2x=120-60 => 3x=60 => x=20.

Answer:John bought the radio with 20, $5 bills and 30-20=10, $2 bills.

Check: 20X5+10X2=100+20=120.

Done.