There are many ways to sum, and only three are introduced for reference:
1, extract the sum of the same integer plus single digits.
25+26+27+28+29
=20×5+5+6+7+8+9
= 100+35
= 135
2, take the middle number multiplied by the number of items.
25+26+27+28+29
=27×5
= 135
3. Calculate with the sum formula of arithmetic sequence.
25+26+27+28+29
=(25+29)×5÷2
= 135