50*1/3×49*2/3=(50+1/3)×(50-1/3)
=2500-1/9
=2499 8/9
同理下题可＝（7＋1／5）×（7－1／5）
＝49－1／25
＝48 24／25
50又1/3*49又2/3
=(50+1/3)(50-1/3)
=50*50-1/3*1/3
=2500-1/9
=2499
7又1/5*6又4/5
=(7+1/5)(7-1/5)
=7*7-1/5*1/5
=49-1/25
=48又24/25
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