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2 + 22 + 222 + 2222 + 22222 + -- + 2222, please use a simple method to calculate
2+22+222+2222+22222+-------+2222222222
=2(1+11+111+...+111111111+1111111111)
=2(123456789+1111111111)
=2*1234567900
=2469135800
Find the rule: (2) 7 8 10 () 22 38
14
Find the rule, fill in 7,8,10, fill in 22,38
7,8,10,14 ,22,38
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