№1
а) 3/5 * 4/9 = 4/15
б)7/9 : 21/25 = 7/9 * 25/21 = 25/27
в)(3/4)^2 = 9/16
№2
а)(5/7) *(21/20 - 7/30) + 16/21 : 8/7 = 5/7 * 49/60 + 16/21 : 8/7 = 7/12 + 2/3 =1,25
б)(1/2 - 1/3)^3 : (1/3 - 1/4)^3 * (3/2)^2 = 1/216 : 1/1728 * 9/4 = 8 * 9/4 = 18
№3
420 - (420 - 420 * 1/3 ) - ((420 - 420 * 1/3 ) * 1/4) = 420 - 140 - 70 = 210 рублей осталось