五年级暑假生活数学 59页
信息发布者：Sarah789
2.
1+3+5+7+9+11+13=7x7=49
1+3+5+7+9+11+13+15+17+19+21=11x11=121
3.
(4+10)x7÷2=49（根）
21+23+25+27+29+31+33+35+37
=21+(23+37)+(25+35)+(27+33)+(29+31)
=21+60x4
=261
4.
1/4+1/8+1/16+1/32+1/64+1/128
=1/4+1/8+1/16+1/32+1/64+1/128+1/128-1/128
=1/4+1/8+1/16+1/32+1/64+1/64-1/128
=1/4+1/8+1/16+1/32+1/32-1/128
=1/4+1/8+1/16+1/16-1/128
=1/4+1/8+1/8-1/128
=1/4+1/4-1/128
=1/2-1/128
=63/128
5.
0.9+0.99+0.999+0.9999+0.99999
=1-0.1+1-0.01+1-0.001+1-0.0001+1-0.00001
=5-0.11111
=4.88889
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