11+12+13+14+15+21+22+23+24+25+31+32+33+34+35+41+42+43+44+45=______

11+12+13+14+15+21+22+23+24+25+31+32+33+34+35+41+42+43+44+45=______.
2025-02-27 23:56:09
推荐回答(1个)
回答1:

11+12+13+14+15+21+22+23+24+25+31+32+33+34+35+41+42+43+44+45
=(11+45)×[(45-11)÷1+1]÷2,
=56×[34+1]÷2,
=56×35÷2,
=980.
故答案为:980