Answer:
Let it be x the number.
We have to sum to x two fifths of him and we know the result is 70, so:
[tex]x + \frac{2}{5}x = 70[/tex]
We could also solve it:
[tex]\frac{5x}{5}+\frac{2x}{5}=\frac{350}{5}[/tex]
[tex]5x + 2x = 350[/tex]
[tex]7x = 350[/tex]
[tex]x=\frac{350}{7}=50[/tex]