Question 1124523
If the tip is 15%, one can multiply the cost by 0.15
or use the first three numbers and half of that, so if the bill is $12.00, the tip is $1.20+0.60 or $1.80.

For tax, use the percentage multiplied by the bill.  For 5% tax, it is half of ten percent which is the first three numbers.  $15.00 bill with 5% tax is $1.50*(1/2) or $0.75.

the final price is the cost+tax+tip.  The tip is not calculated using the cost and tax, only the cost alone.