Twenty dollar bills...

Question

Brad has $700 in $10bills and $20bills. If he has two more twenties then tens, how many $20 bills does he have?

Answer 1

Let x represent the number of 10 dollar bills and y represent the number of 20 dollar bills.  Then we need to set up a system of equations and solve.

"Brad has $700 in $10bills and $20bills."  In equation form, this looks like

 

700 = 10x + 20y     (equation 1)

 

because 10x gives us the amount of money we have in 10 dollar bills, and 20y gives us the amount of money we have in 20 dollar bills.  

"he has two more twenties then tens."  In equation form, this looks like

 

y = x + 2   (equation 2)

 

because the number of of twenties he has, y, is two more than the amount of tens he has.  Then to solve, we can substitute equation 2 into equation 1:

 

700 = 10x + 20y           (1)

700 = 10x + 20(x+2)

 

Now we can simplify this and solve for x.  Once we have x, we can substitute the value of x into equation 2 to find y.

 

Let me know if you would like any clarification.