Question 4161
If you leave a 20% tip for the waiter for a $100.00 check, that will be 20% of $100.00.  Change the percentage to a decimal by dividing 20 by 100, this comes to 0.2 then multiply this by the amount of the check ($100.00).  The waiter's tip would be 0.2($100.00) = $20.00

Similarly for the captain's tip of 10%.  0.1($100.00) = $10.00

The final bill would be:  $100.00 + $20.00 + $10.00 = $130.00