Samuel has $5, $10, and $20 bills which amount to $150 in his wallet. His $10-bills amount to $50, and he has 4 $20-bills. How many bills does Samuel have in his wallet?
His $20 bills amount to 4 x $20 = $
<gadget id="calculator">4*20</gadget>
<output>80</output>
80.
So the total amount of the $10 and $20 bills is $80 + $50 = $
<gadget id="calculator">80+50</gadget>
<output>130</output>
130.
Hence, the remaining $5 bills amount to $150 - $130 = $20.
This means that there are $20/$5 = 
<gadget id="calculator">20/5</gadget>
<output>4</output>
4 $5 bills.
There are also $50/$10 = 5 $10 bills.
Therefore, Samuel has 4 + 4 + 5 = 
<gadget id="calculator">4+4+5</gadget>
<output>13</output>
13 bills in his wallet.

<result>13</result>