A delivery truck

A box delivery truck consumes 12 gallons of gasoline in three days. 2 4/5 gallons of gas is consumed on the first day, and three and 7/10 gallons are consumed on the second day. How much is consumed on the third day?

Correct answer:

c =  5 ¹⁄₂ = 11/2

Step-by-step explanation:

$$\begin{gathered} V=12\text{gal} \\ a=2\frac{4}{5}=2+\frac{4}{5}=\frac{2\cdot 5+4}{5}=\frac{10+4}{5}=\frac{14}{5}=2\frac{4}{5}=2.8\text{gal} \\ b=3\frac{7}{10}=3+\frac{7}{10}=\frac{3\cdot 10+7}{10}=\frac{30+7}{10}=\frac{37}{10}=3\frac{7}{10}=3.7\text{gal} \\ V=a+b+c \\ c=V-a-b=12-\frac{14}{5}-\frac{37}{10}=\frac{11}{2}=5\frac{1}{2}=5.5 \end{gathered}$$

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