18 21/53*27/34*42 2/5*47 2/9-125/161*8 216/617*15 17/40*22 31/36 ! !

1) 18 21/53 * 27/34 = (975*27)/(53*34)=
=26325/1802= 14 1097/1802

2)14 1097/1802 * 42 2/5 = (26325*212)/(1802*5) =
=(5265*2)/(17*1)= 10530/17= 619 7/17

3) 619 7/17 * 47 2/9 = (10530*425)/ (17*9) =
=(1170*25)/(1*1)=29250

4) 125/161 * 8 216/617 = ( 125*5152)/(161*617)=
= (125*32)/(1*617) = 4000/617=6 298/617

5) 6 298/617 * 15 17/40 = (4000*617)/(617*40) = 100

6) 100* 22 31/36 = (823*100)/(36*1)=
= (823*25)/(9*1)= 20575/9 = 2286 1/9

7) 29250 - 2286 1/9 = 26963 8/9

ответ: 26963 8/9 .