Answer:
[tex]\displaystyle \: \: \: \: 7 \\ \: \: \sum \: (10n + 10) \\ n = 1[/tex]
Step-by-step explanation:
You can use Summation Notation as a pattern to evaluating "20 + 30 + 40 + 50 + 60 + 70 + 80":
[tex]\displaystyle \: \: \: \: 7 \\ \: \: \sum \: (10n + 10) \\ n = 1[/tex]
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