use mental math to approximate what a 15% tip would be for a bill of $31.99.\na. $3.20\nb. $4.80\nc…

Explanation:

Step1: Round the bill amount

Round $31.99$ to $32$.

Step2: Calculate 10% of the rounded - amount

10% of 32 is $\frac{10}{100}\times32 = 3.2$.

Step3: Calculate 5% of the rounded - amount

5% is half of 10%, so 5% of 32 is $\frac{3.2}{2}=1.6$.

Step4: Calculate 15% of the rounded - amount

15% = 10%+5%, so 15% of 32 is $3.2 + 1.6=4.8$.

Answer:

B. $4.80$