1ц3/7
2/5×12=2/5×12/1=24/5=4ц4/5
2ц7/9×15=25/9×15/1=375/9=41ц6/9=41ц2/3
3ц1/3÷30=10/3÷30/1=10/3×1/30=10/90=1/9
7050. 7049........7050........7051
18200. 18199........18200....18201
19999. 19998 ...19999........20000
14799. 14798....14799....14800
<span>8000. 7999...........8000.............8001
199690 199689.........199690..........199691
10000. 9999..........10000........10001
49999. 49998.........49999.........50000</span>
1 + 2 + 3 + ......+ 2005 + 2006 + 2007=(1+2006)+(2+2005)+(3+2004)+...+2007каждое слагаемое делится на 2007, значит и сумма делится на 2007
<span>20 7/19 - (3 1/19 + 5 5/19) = 12 1/19
1) 3 1/19 + 5 5/19 = 8 6/19
2) 20 7/19 - 8 6/19 = 12 1/19</span>