1/3-1/5 = ( 1 * 5 ) / (3 * 5) - ( 1 * 3 ) / (5 * 3) = 5/15 - 3/15 = 2/15
<span>1/3-1/6 = ( 1 * 2 ) / (3 * 2) - 1 / 6 = 2/6 - 1/6 = 1/6 </span>
<span>1/4-1/7 = ( 1 * 7 ) / ( 4 * 7) - (1 * 4 ) / ( 7 * 4 ) = 7/28 - 4/28 = 3/28
</span>понятно 6 или 7 класс!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
Х-утром,6х-днем,3х-вечером
х+6х+3х=20
10х=20
х=2-утром
6*2=12-днем
3*2=6-вечером
7*20= 140
200-140=60
ну во.
<span>27:х+405:9=48
27:х+45=48
27:х=48-45
27:х=3
х=27:3
х=9</span>