Quickly it is.
1/2 of the sugar to bake the cake, 3/8 of it to make tarts, means we've used
[tex]\dfrac 1 2 + \dfrac 3 8 = \dfrac 4 8 + \dfrac 3 8 = \dfrac 7 8[/tex]
so there's only
[tex] 1-\dfrac 7 8= \dfrac 1 8[/tex]
left.
That's the fraction left; the amount of sugar left is
[tex]\dfrac 1 8 \cdot \dfrac 4 5 = \dfrac 1 {10} = 0.1 \textrm{ kg}[/tex]
I forgot Q16.
Let c be the capacity of the jug
[tex]\dfrac 4 9 c + 650 = \dfrac 4 5 c[/tex]
[tex]650 = \dfrac 4 5 c - \dfrac 4 9 c = \dfrac{36c}{45} - \dfrac{20c}{45}=\dfrac{16c}{45}[/tex]
[tex]\dfrac{45}{16}(650) = \dfrac{14625}{8} \approx 1828.1[/tex]
Check: I'll check the exact answer; I don't like approximations.
[tex] \dfrac{4}{9}\cdot\dfrac{14625}{8} = \dfrac{1625}{2}[/tex]
[tex] \dfrac{4}{5}\cdot\dfrac{14625}{8} = \dfrac{2925}{2}[/tex]
[tex]\dfrac{2925}{2}-\dfrac{1625}{2} =\dfrac{1300}{2} = 650 \quad\checkmark[/tex]
