The tractor

The tractor sows an average of 1.5 ha per hour. How many hours does it sow a rectangular trapezoid field with 635m and 554m bases and a long arm of 207m?

Correct answer:

t =  7.5499 h

Step-by-step explanation:

$$\begin{gathered} a=635\text{n} \\ c=554\text{m} \\ b=207\text{m} \\ h=\sqrt{b^2-(a-c{)}^2}=\sqrt{207^2-(635-554{)}^2}=72\sqrt{7}\text{m}\doteq 190.4941\text{m} \\ S=\frac{a+c}{2}\cdot h=\frac{635+554}{2}\cdot 190.4941\doteq 113248.7391{\text{m}}^2 \\ {S}_1=S\to \text{ha}=S:10000\text{ha}=113248.7391:10000\text{ha}=11.32487\text{ha} \\ t=S_1/1.5=11.3249/1.5=7.5499\text{h} \end{gathered}$$

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