49.7+59.7+69.7+.+99.7+109.7简算

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49.7+59.7+69.7+.+99.7+109.7简算
49.7+59.7+69.7+.+99.7+109.7简算

49.7+59.7+69.7+.+99.7+109.7简算
49.7+59.7+69.7+.+99.7+109.7
=50-0.3+60-0.3+70-0.3+80-0.3+90-0.3+100-0.3+110-0.3
=(50+60+70+80+90+100+110)-0.3×7
=560-2.1
=557.9

(49.7+109.7)x7/2
=(50-0.3+110-0.3)x7/2
=160x7/2-0.6x7/2
=560-2.1
=557.9