the question in English
Carlos paid a $ 300 bill with $ 5 and $ 10 bills. In total 45 bills to make the payment. How many tickets did Carlos use?
let
x------> quantity of $5 bills
y------> quantity of $10 bills
we know that
x+y=45------>x=45-y-----> equation 1
5x+10y=300----> equation 2
substitute the equation 1 in equation 2
5*[45-y]+10y=300----> 225-5y+10y=300----> 5y=75----> y=15
x=45-y-----> x=45-15-----> x=30
the answer is
quantity of $5 bills is 30
quantity of $10 bills is 15
the answer in Spanish
Hagamos
x------> cantidad de billetes de $5
y------> cantidad de billetes de $10
Sabemos que
x+y=45------>x=45-y-----> ecuacion 1
5x+10y=300----> ecuacion 2
sutituya la ecuacion 1 en la ecuacion 2
5*[45-y]+10y=300----> 225-5y+10y=300----> 5y=75----> y=15
x=45-y-----> x=45-15-----> x=30
la respuesta es
cantidad de billetes de $5 es 30
cantidad de billetes de $10 es 15