Linear Equation #1

Algebra Level 3

Farmer Joe can pull an empty handcart for a distance of 60 km 60\text{ km} a day. If the cart is full of grains, he can only pull it for a distance of 40 km 40\text{ km} a day.

Now, Joe takes 3 days to make 2 round trips between his home and the warehouse, leaving home with the cart full of grains and coming back home with an empty cart.

How long does it take (in hours) for Joe to go to the warehouse from his home with an empty handcart?


Clarification: One day equals 24 hours.


Source: This problem is from a book <구일집(九一集)> made in Chosun (old Korea), 1724.


The answer is 14.4.

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1 solution

Boi (보이)
Jun 16, 2017

Let the distance between the warehouse and the house be x km x\text{km} .

Then we can see that

x 60 + x 40 + x 60 + x 40 = 3 \dfrac{x}{60}+\dfrac{x}{40}+\dfrac{x}{60}+\dfrac{x}{40}=3

x 30 + x 20 = 3 \dfrac{x}{30}+\dfrac{x}{20}=3

5 x 60 = 3 \dfrac{5x}{60}=3

x = 36 x=36

Therefore the distance is 36 km 36\text{km} .


So, Joe needs 36 km 60 km/day = 6 10 day = 144 10 hours = 14.4 hours \dfrac{36\text{km}}{60\text{km/day}}=\dfrac{6}{10}\text{day}=\dfrac{144}{10}\text{hours}=\boxed{14.4\text{hours}}

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