Пусть х - тетрадей по 12 листов, тогда 60-х - тетрадей по 18 листов, всего листов 840, значит
12*х + 18*(60-х) = 840
12х+1080-18х=840
-6х=-240
х=40 (тетрадей по 12 листов)
соответвенно 60-40=20 тетрадей по 18 листов<span><span> 19 Нравится</span><span> <span>Пожаловаться</span></span></span>
3^12/(3^5)^2=3^(12-5*2)=3^2=9
2.7х-3-х-0.6=-0.2
1.7х=3.4
х=2
7-3.1+0.1у=-0.2у
3.9=-0.3у
у=-13
![(2x-1)(3x+7)-(1+6x)(x+2)=4](https://tex.z-dn.net/?f=%282x-1%29%283x%2B7%29-%281%2B6x%29%28x%2B2%29%3D4)
![6x^{2}+14x-3x-7-x-2-6x^{2}-12x=4](https://tex.z-dn.net/?f=6x%5E%7B2%7D%2B14x-3x-7-x-2-6x%5E%7B2%7D-12x%3D4%C2%A0)
![6x^{2}+14x-3x-7-x-2-6x^{2}-12x-4=0](https://tex.z-dn.net/?f=6x%5E%7B2%7D%2B14x-3x-7-x-2-6x%5E%7B2%7D-12x-4%3D0)
![(6x^{2}-6x^{2})+(14x-3x-x-12x)+(-7-2-4)=0](https://tex.z-dn.net/?f=%286x%5E%7B2%7D-6x%5E%7B2%7D%29%2B%2814x-3x-x-12x%29%2B%28-7-2-4%29%3D0)
![-2x-13=0](https://tex.z-dn.net/?f=-2x-13%3D0)
![2x=-13](https://tex.z-dn.net/?f=2x%3D-13)
![x=-13:2](https://tex.z-dn.net/?f=x%3D-13%3A2)
![x=-6,5](https://tex.z-dn.net/?f=x%3D-6%2C5)
__________________________________________________________________
![(2\cdot(-6,5)-1)\cdot(3\cdot(-6,5)+7)-(1+6\cdot(-6,5))\cdot(-6,5+2)=4](https://tex.z-dn.net/?f=%282%5Ccdot%28-6%2C5%29-1%29%5Ccdot%283%5Ccdot%28-6%2C5%29%2B7%29-%281%2B6%5Ccdot%28-6%2C5%29%29%5Ccdot%28-6%2C5%2B2%29%3D4)
![(-13-1)\cdot(-19,5+7)-(1-39)\cdot(-4,5)=4](https://tex.z-dn.net/?f=%28-13-1%29%5Ccdot%28-19%2C5%2B7%29-%281-39%29%5Ccdot%28-4%2C5%29%3D4)
![-14\cdot(-12,5)-(-38)\cdot(-4,5)=4](https://tex.z-dn.net/?f=-14%5Ccdot%28-12%2C5%29-%28-38%29%5Ccdot%28-4%2C5%29%3D4)
![175-171=4](https://tex.z-dn.net/?f=175-171%3D4)
![4=4](https://tex.z-dn.net/?f=4%3D4)