To calculate a 15% tip on a $24 bill a customer adds $2.40 and half of $2.40, or $1.20, to get $3.60. Is this method valid? Why or why not?

Answer 1

Yes. That's the way I calculate a tip.

10% of 24 is 2.40.
Half of 2.40 is 1.20.

2.40 + 1.20 = 3.60

Answer 2

10% + half of 10% = 15%