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Периметр прямоугольника= 10+10+5+5=30
5*5*5*5*5=3125
20% от 3125=3125:100*20=625
18 : (16 - 7) * 2 = 18 : 9 * 2 = 18 : 9 * 2 = 2 * 2 = 4
1) (36*21)/12=3*21=63
2) (40*420)/60=40*7=280
3) (5*6*78)/3=5*2*78=10*78=780
4) (45*63)/81=(45/9*63/9)=5*7=35