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100×10-(100-2×x-60)×10=900


Răspuns :

[tex]100 \times 10 - (100 - 2 \times x - 60) \times 10 = 900 \: | \div 10[/tex]

[tex]100 - (100 - 2x - 60) = 90[/tex]

[tex]100 - 100 + 2x + 60 = 90[/tex]

[tex]2x = 90 - 60[/tex]

[tex]2x = 30 \: | \div 2[/tex]

[tex]x = 15[/tex]