In a class of 25 students , 10 have less than 6 marbles, 10 have more than 7 marbles and 4 have more than 8 marbles. How many students have more than 5 marbles but less than 9 Marbles? (set)

$$\begin{gathered} Total SP=(50\times 48)+(50\times 48) = 4,800 \\ Total CP =(50\times \frac{48}{1.2})+(50\times \frac{48}{0.8})=5,000 \\ \therefore Net Loss = 5,000-4800=Tk 200 \mathit{a}\mathit{n}\mathit{s}\mathbf{.} \end{gathered}$$

$$\begin{gathered} Here, blue paint and yellow paint ratio is 1 : 2 \\ Let \text{'}x\text{'} is the usage of per kg paint which is general term of the ratio \\ Blue paint = 1\times x kg \\ Yellow paint=2\times xkg \\ According to the question, \\ 3x \times 120-(110\times x+100\times 2x)=2,000 \\ \Rightarrow 360x-310x=2,000 \\ \Rightarrow 50x=2,000 \\ \therefore x=40 \\ Yellow paint usage=2\times 40=80 kg \mathit{a}\mathit{n}\mathit{s}\mathbf{.} \end{gathered}$$

Let, 1^st day sail=y hours and 2^nd day= 7-y

According to the first condition, y-(7-Y)=3

y=5

So, 1^st day sail = 5 & 2^nd day said = 5-3= 2

Again, speed of 2^nd day and speed of 1^st day = x-5

According to the first condition, 

$$\begin{gathered} 2\times x+5\left(x-5\right)=59 \\ \Rightarrow 7x=59+25=84 \\ \therefore x=\frac{84}{7}=12 \\ {2}^{nd} day speed = 12 kmph \mathit{a}\mathit{n}\mathit{s}\mathbf{.} \end{gathered}$$