13*29中13个位是3,3*2+9=15,3*9=27,so13*29=377后面差不多,11*39:3+9=12,3/9分别在首尾,满十进一,11*39=429
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13×29 = 13×(30-1)= 13×30 - 13 = 390 - 13 = 377
26×19 = 26×(20-1)= 26×20 - 26 = 520 - 26 = 496
11×39 = (10+1)×39= 10×39 + 39 = 390 + 39 = 429