А) 91×8 = (90+1)×8 = 90×8+1×8 = 720+8 = 728
б) 7×59 = 7×(60-1)= 7×60-7×1 = 420-7 = 413
в) 6×52 = 6×(50+2) = 6×50+6×2 = 300+12 = 312
г) 198×4= (200-2)×4 = 200×4-2×4 = 800-8 = 792
д) 202×3 = (200+2)×3 = 200×3+2×3 = 600+6 = 606
е) 397×5 = (400-3)×5 = 400×5-3×5 = 2000-15 = 1985
ж) 24×11 = (20+4)×11 = 20×11+4×11 = 20×11+44 = (10+10)×11+44 = 11×10+11×10+44 = 110+110+44 = 220+44 = 264
з) 35×12 = (30+5)×12 = 30×12+5×12 = (10+20)×12+60 = 10×12+20×12+60 = 20×12+120+60 = (10+10)×12+180 = 12×10+12×10+180 = 120+120+180 = 240+ 180 = 420
и) 4×505 = 4×(500+5) = 4×500+4×5 = 2000+20 = 2020
к) 25×399 = 25×(400-1) = 25×400-25×1 = 1000-25 = 9975