Explicație pas cu pas:
S=1+2+3+....+n=n(n+1)/2
n=10/100×n(n+1)/2=>n=10n(n+1)/200 => n= n(n+1)/20 => 20n=n(n+1)=> n+1=20 => n=19
Răspuns: [tex]\bf \red{\underline{n = 19}}[/tex]
Explicație pas cu pas:
[tex]\bf S = 1+2+3+......+n[/tex]
[tex]\bf S =\dfrac{n\cdot(n+1)}{2}[/tex]
[tex]\bf n= 10\%\cdot S\Rightarrow n = \dfrac{10}{100}\cdot\dfrac{n\cdot(n+1)}{2}\Rightarrow[/tex]
[tex]\bf n = \dfrac{10\cdot n\cdot(n+1)}{100\cdot2}\Rightarrow n= \dfrac{n\cdot(n+1)}{10\cdot2}\Rightarrow[/tex]
[tex]\bf \Rightarrow 20\cdot n=n\cdot(n+1)~~~\bigg|:n[/tex]
[tex]\bf 20=n+1\Rightarrow n = 20-1\Rightarrow \red{\underline{n = 19}}[/tex]
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