Land division calculation

The king divided part of his lands between his three sons. To the first, he gave one-fifth. To the second, he gave 40 ha less than the first, and to the third, he gave 30% of the whole. Write down what part of the land was left to the king.
Calculation using variables.

Final Answer:

x = 0.3a+40

Step-by-step explanation:

$$\begin{gathered} x=a-a/5-(a/5-40)-0.30a \\ x=0.3a+40 \end{gathered}$$

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