21) 2$$\frac{3}{17}$$: (6$$\frac{5}{17}$$+1$$\frac{12}{17}$$)-(4$$\frac{2}{5}$$-2$$\frac{3}{5}$$):5;

2$$\frac{3}{17}$$ = $$\frac{2*17+3}{17}$$ = $$\frac{37}{17}$$ 6$$\frac{5}{17}$$ = $$\frac{6*17+5}{17}$$ = $$\frac{107}{17}$$ 1$$\frac{12}{17}$$ = $$\frac{1*17+12}{17}$$ = $$\frac{29}{17}$$ 4$$\frac{2}{5}$$ = $$\frac{4*5+2}{5}$$ = $$\frac{22}{5}$$ 2$$\frac{3}{5}$$ = $$\frac{2*5+3}{5}$$ = $$\frac{13}{5}$$ 1) (6$$\frac{5}{17}$$+1$$\frac{12}{17}$$) = $$\frac{107}{17}$$ + $$\frac{29}{17}$$ = $$\frac{136}{17}$$ = 8 2) (4$$\frac{2}{5}$$-2$$\frac{3}{5}$$) = $$\frac{22}{5}$$ - $$\frac{13}{5}$$ = $$\frac{9}{5}$$ = 1,8 3) 1,8 : 5 = 0,36 4) 8 - 0,36 = 7,64 5) 2$$\frac{3}{17}$$ : 7,64 = $$\frac{37}{17}$$ : 7,64 = $$\frac{37}{17}$$ : $$\frac{764}{100}$$ = $$\frac{37}{17}$$ * $$\frac{100}{764}$$ = $$\frac{3700}{12988}$$ = $$\frac{925}{3247}$$ ≈ 0,285 Ответ: $$\frac{925}{3247}$$ ≈ 0,285