Solución
Para el primer inciso se tiene : <img src="https://tex.z-dn.net/?f=%5Cfrac%7B2%7D%7B3%7D%2B%5Cfrac%7B5%7D%7B17%7D%3D%5Cfrac%7B%2817%29%282%29%2B%283%29%285%29%7D%7B%283%29%2817%29%7D%3D%5Cfrac%7B34%2B15%7D%7B51%7D%3D%5Cfrac%7B49%7D%7B51%7D%5C%5C%5Cfrac%7B2%7D%7B3%7D-%5Cfrac%7B1%7D%7B10%7D%3D%5Cfrac%7B17%7D%7B30%7D" /> luego <img src="https://tex.z-dn.net/?f=%28%5Cfrac%7B49%7D%7B51%7D%29%28%5Cfrac%7B17%7D%7B30%7D%29%3D%5Cfrac%7B49%7D%7B90%7D" /> por lo tanto <img src="https://tex.z-dn.net/?f=%5Cfrac%7B2%7D%7B3%7D%2B%5Cfrac%7B5%7D%7B17%7D%2A%5Cfrac%7B2%7D%7B3%7D-%5Cfrac%7B1%7D%7B10%7D%3D%5Cfrac%7B49%7D%7B90%7D" />
Para el segundo inciso se obtiene : <img src="https://tex.z-dn.net/?f=%5Cfrac%7B5%7D%7B7%7D%2B%5Cfrac%7B1%7D%7B4%7D%3D%5Cfrac%7B27%7D%7B28%7D%5C%5C%5Cfrac%7B5%7D%7B8%7D%5Cdiv%5Cfrac%7B1%7D%7B4%7D%3D%5Cfrac%7B5%7D%7B2%7D%5C%5C%5Cfrac%7B27%7D%7B28%7D%5Cdiv%5Cfrac%7B5%7D%7B2%7D%3D%5Cfrac%7B27%7D%7B70%7D" />
Por lo tanto <img src="https://tex.z-dn.net/?f=%5Cfrac%7B5%7D%7B7%7D%2B%5Cfrac%7B1%7D%7B4%7D%5Cdiv%28%5Cfrac%7B5%7D%7B8%7D%5Cdiv%5Cfrac%7B1%7D%7B4%7D%29%3D%5Cfrac%7B27%7D%7B70%7D" />
Para el último inciso se.
Tiene : <img src="https://tex.z-dn.net/?f=%28%5Cfrac%7B1%7D%7B2%7D-%5Cfrac%7B1%7D%7B3%7D%29%3D%5Cfrac%7B%283%29%281%29-%282%29%281%29%7D%7B6%7D%3D%5Cfrac%7B3-2%7D%7B6%7D%3D%5Cfrac%7B1%7D%7B6%7D%5C%5C%5Cfrac%7B1%7D%7B6%7D%2B%5Cfrac%7B1%7D%7B2%7D%3D%5Cfrac%7B%282%29%281%29%2B%286%29%281%29%7D%7B6%7D%3D%5Cfrac%7B2%2B6%7D%7B6%7D%3D%5Cfrac%7B8%7D%7B6%7D%3D%5Cfrac%7B4%7D%7B3%7D" /> , es decir <img src="https://tex.z-dn.net/?f=%28%5Cfrac%7B1%7D%7B2%7D-%5Cfrac%7B1%7D%7B3%7D%29%2B%5Cfrac%7B1%7D%7B2%7D%3D%5Cfrac%7B4%7D%7B3%7D" />.
Saludos.