(1) |
5+10+15+20+25+
30+35+40
=(5+40)x8÷2
=180
|
(2) |
1+3+5+7+9+11+13+
15+17+19+21+23
=(1+23)x12÷2
=144
|
(3) |
1-1/2-1/4-1/8-1/16-1/32 =1-(1-1/2)-(1/2-1/4)-(1/4-1/8)-(1/8-1/16)-(1/16-1/32) =1/32 |
解法一 |
最下一层有7x(10-1)x2=25根
(7+25)x10÷2=160(根)
|
解法二 | 7+9+11+13+15+17+19+21+23+25=160(根) |