3 рубашки - это 90% от стоимости куртки
4 рубашки - это 120% от стоимости куртки: 4х90:3=120
Ответ: 4 рубашки дороже куртки на 20%
Приводим к общему знаменателю и вычисляем.
2/3 + 5/8 = 16/24 + 15/24 = 31<span>/24
7</span>/12 - 3/8 = 14/24 - 9/24 = 5<span>/24
</span><span>11/16 - 5/8 = </span>11/16-10/16 = 1/<span>16
</span><span>5/35 + 3/10 = </span>10/70 + 21/70 = 31/<span>70
</span><span>8/15 - 4/9 = </span>24/45 - 20/45 = <span>4/45
</span><span>4/15 + 7/12 = </span>16/60 + 35/60 = <span>51/60
</span><span>11/48 - 5/36 = </span>33/144 - 20/144 = <span>13/144
</span><span>4/5 - 2/3 + 4/15 = </span>12/15 - 10/15 + 4/15 = <span>6/15
</span><span>7/8 + 11/12 - 5/6 = </span>21/24 + 22/24 - 20/24 = <span>23/24</span><span />
<em>12у - 7у = 315</em>
<em>5у = 315</em>
<em>у = 315 : 5 </em>
<em>у = 63</em>
23,6+(14,5-30,1)-(6,8+1,9)=23,6-15,6-8,7=-0,7