пуст телевизор х руб тогда магнитафон (х-520)руб
1)<span>1/12+3 4/15</span>=3+<span>1/12</span>+<span>4/15</span> = 3+<span>1·5/12·5</span>+<span>4·4/15·4</span>=3+<span>5/60</span>+<span>16/60</span>=3+ <span>5+1660</span>=3 <span>21/60</span>=3 <span>7·3/20·3</span>=3 <span>7/20</span> = 3.35
2)3 19/21+2 2/3=5+<span>19/21</span>+<span>2/3</span>=5+<span>19·1/21·1</span>+<span>2·7/3·7</span>=5+1<span>9/21</span>+<span>14/21</span>=5+ <span>19+14/21</span>=5 <span>33/21</span>=5 11·3/7·3=5 <span>11/7</span>=5 <span>4+1·7/7</span>=6 <span>4/7
</span>3)5*5 4/5=5·4+5·5/5=5<span>·</span><span>29/5</span> = <span>5·29/5</span> = <span>145/5</span> = <span>29·5/5</span><span> = 29
</span>И все в таком роде
4)<span>1 7/9*1 2/3=2 26/27
</span>5)<span>5 1/10-1 1/16=4 3/80
</span>6)<span>4-2/7=3 5/7
</span>7)<span>4/9+1 2/3=2 1/9
</span>8)5 3/8-2 11/16=2 11/16
40+х=250-140
40+х=110
х=110-40
Х=70
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40+70=250-140
110=110
а-90=310+310
а-90=620
а=620+90
а=710
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710-90=310+310
620=620
590-х=110+210
590-х=320
х=590-320
х=270
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590-270=110+210
320=320
с-40=130+190
с-40=320
с=320+40
с=360
_________________
360-40=130+190
320=320
х+120=900-540
х+120=360
х=360-120
х=240
________________
240+120=900-540
360=360
480+в=960-150
480+в=810
в=810-480
в=330
______________
480+330=960-150
810=810
Площадь поверхности прямоугольного параллелепипеда
S=(11*9+9*3+11*3)*2=318
2) 2,5:5=0,5
6) 0,24:8=0,03
2) 8,715:21=0,415
6) 8,652:721=0,012