1+4+7+10+13+16+19+22+25+28+31+34+37+40+43+46+49 用脱式计算

425

8×50+25＝425

1+4+7+10+13+16+19+22+25+28+31+34+37+40+43+46+49
=(1+49)+(4+46)+(7+43)+(10+40)+(13+37)+(16+34)+(19+31)+(22+28)+25
=50*8+25
=400+25
=425

1+4+7+10+13+16+19+22+25+28+31+34+37+40+43+46+49
=5+7+10+13+16+19+22+25+28+31+34+37+40+43+46+49
=12+10+13+16+19+22+25+28+31+34+37+40+43+46+49
=22+13+16+19+22+25+28+31+34+37+40+43+46+49
=35+16+19+22+25+28+31+34+37+40+43+46+49
=51+19+22+25+28+31+34+37+40+43+46+49
=70+22+25+28+31+34+37+40+43+46+49
=92+25+28+31+34+37+40+43+46+49
=117+28+31+34+37+40+43+46+49
=117+28+31+34+37+40+43+46+49
=145+31+34+37+40+43+46+49
=176+34+37+40+43+46+49
=176+34+37+40+43+46+49
=210+37+40+43+46+49
=210+37+40+43+46+49
=247+40+43+46+49
=287+43+46+49
=330+46+49
=376+49
=425
简算
1+4+7+10+13+16+19+22+25+28+31+34+37+40+43+46+49
=（1+49）16/2+25
=400+25
=425