Answer:
[tex]\boxed{\text{40 \$1 bills and 8 \$5 bills}}[/tex]
Step-by-step explanation
Let f = the number of $5 bills
and o = the number of $1 bills
You have a system of two equations:
[tex]\begin{cases}(1)& 5f = o\\(2) & f + o = 48\\\end{cases}[/tex]
[tex]\begin{array}{lrcll}(3) & f + 5f & = & 48 &\text{Substituted (1) into (2)}\\ & 6f & = & 48 &\text{Combined like terms}\\(4)& f & = & \mathbf{8} &\text{Divided each side by 6}\\& o & = & 5\times 8 &\text{Substituted (4) into (1)} \\& o& = &\mathbf{40} &\\\end{array}\\\text{Dan has $\boxed{\textbf{40 \$1 bills and 8 \$5 bills}}$}[/tex]
Check:
[tex]\begin{array}{rclcrcl}5\times 8 & = & 40 & \qquad & 8 + 40 &=& 48\\40 & = & 40 & \qquad & 48 & = & 48\\\end{array}[/tex]
OK.
