Solution:
Note :In such type of questions use allegation method to save your valuable time.

Required number of males
= $$\frac{8000}{(1 + 1)}$$  × 1
= 4000

Solution:
Total number of passenger in each compartment = $$\frac{{ {25 \times 7} }}{5}$$  = $$35$$
Total berth = 35² = 1225
Maximum available capacity
$$\eqalign{ = \frac{{ {1225 \times 80} }}{{100}} \cr = 980\,{\text{seats}} \cr} $$

Solution:
Percentage of failed students = 25%
∴ Percentage of passed students
= (100 - 25)% = 75%
According to the question,
Total students :
= $$\frac{450}{75}$$ × 100 = 600

Solution:
Let the original quantity be x kg.
Vanaspati ghee in x kg
$$\eqalign{ = \left( {\frac{{40}}{{100}}x} \right){\text{kg}} \cr = \left( {\frac{{2x}}{5}} \right){\text{kg}} \cr} $$
Now,
$$\eqalign{ \Rightarrow \frac{{\frac{{2x}}{5}}}{{x + 10}} = \frac{{20}}{{100}} \cr \Rightarrow \frac{{2x}}{{5x + 50}} = \frac{1}{5} \cr \Rightarrow 5x = 50 \cr \Rightarrow x = 10 \cr} $$

Solution:
= 10% of 5 + 5% of 10
= $$\left( {\frac{{10}}{{100}} \times 5} \right)$$   + $$\left( {\frac{{5}}{{100}} \times 10} \right)$$
= 0.5 + 0.5
= 1.0

Solution:
Let Mr. More's monthly income be Rs. $$x$$
Then,
[100 - (40 + 30)]% of [100 - 20 + 15]% of $$x$$ = 8775
⇒ 30% of 65% of $$x$$ = 8775
⇒ $$\left( {\frac{{30}}{{100}} \times \frac{{65}}{{100}} \times x} \right)$$   = 8775
⇒ $$\frac{39}{200}$$ $$x$$ = 8775
⇒ $$x$$ = $$\left( {\frac{{8775 \times 200}}{{39}}} \right)$$
⇒ $$x$$ = 45000

Solution:
20% = $$\frac{1}{5}$$ = $$\frac{4}{5}$$
X  :   Y
4   :   5
Let X = 4a
    Y = 5a
Hence,
⇔ $$\frac{Y - X}{Y}$$
= $$\frac{5a - 4a}{5a}$$
= $$\frac{a}{5a}$$
= $$\frac{1}{5}$$
⇔ $$\frac{X}{X - Y}$$
= $$\frac{4a}{4a - 5a}$$
= $$\frac{4a}{- a}$$
= - 4
Hence required answer = $$\frac{1}{5}$$, - 4