Hi Danielle,
A tip of 15% is easy to calculate. You can do it in your head, especially if you round to the nearest $0.10 at each step. What I do is think of 15% as 10% plus 5%. For example if the bill is $30.29 then what I do is
10% of $30.29 is onetenth of $30.29 so just move the decimal one place left to get $3.029
I think of this as $3.00
5% is half of 10% and half of $3.00 is $1.50
Hence I would leave a tip of $3.00 + $1.50 = $4.50.
Viviana's calculation is a little different. She keeps better track and then rounds up to the nearest $0.05, so her calculation are
10% of $30.29 is $3.029
5% of
$30.29 is half of $3.029 or $1.5145
Thus 15% of $30.29 is $3.029 + $1.5145 = $4.5435
Rounding up to the nearest nickel gives a tip of $4.55
Penny
