Quantity of alcohol in 10 c.c. solution
= (20% of 6 + 60% of 4) c.c.
= $$\left( {\frac{{20}}{{100}} \times 6 + \frac{{60}}{{100}} \times 4} \right)$$    c.c.
= (1.2 + 2.4) c.c.
= 3.6 c.c.
∴ Required strength :
$$\eqalign{ & = \left( {\frac{{3.6}}{{10}} \times 100} \right)\% \cr & = 36\% \cr} $$

Let re are X books in library.
Number of Hindi books = 60% of X = $$\frac{{60{\text{X}}}}{{100}}$$  = 0.6X
Remaining Books = X - 0.6X = 0.4X
Number English books = 40% of reaming books = 60% of 0.4X = 0.24X.
Urdu Books = X-0.6X -0.24X = 0.16X
Given,
0.24X = 3600
X $$ = \frac{{3600}}{{0.24}} = 15000$$
Urdu Books = 0.16X = 0.16 × 15000 = 2400

Money spent originally = Rs. 140
Less Money to be spent now
= 10% of 140
= Rs. 14
Rs. 14 now yield 500 gm sugar
So, Present rate of sugar = Rs. 28 per kg.
If present value is Rs. 90, original value = Rs. 100
If present value is Rs. 28 original value
$$ = {\text{Rs}}{\text{. }}\frac{{100}}{{90}} \times 28 = {\text{Rs}}{\text{. }}31.11$$

Let initial cost of raw material be 100. So, initial labor cost was 25 and net cost was 125
Now,
15% increment in raw materials cost and labor cost has gone up to 30% from 25 %
Raw material cost = 115 And
Labor cost = (115 × 30%) = 34.5
So, New net cost,
= 115 + 34.5 = 149.5
Difference of labor cost = 149.5 - 125 = 24.5
% reduction = $$\frac{{24.5 \times 100}}{{149.5}}$$   = 17%(approx.)

Let his original salary be Rs. 100
Salary after increment = Rs. 120
Let tax on original salary be 20% and now tax on increased salary (Rs. 20) will be 22% i.e. Rs. 4.40
Thus, increase in tax liability $$ = \frac{{4.40}}{{20}} \times 100 = 22\% $$

= 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

$$\eqalign{ & 78\% \,{\text{of}}\,\,750 + 34\% \,{\text{of}}\,x = 30\% \,{\text{of}}\,\,2630 \cr & or,\, {\frac{{ {78 \times 750} }}{{100}}} + \frac{{34x}}{{100}} = \left( {30 \times 2630} \right) \times 100 \cr & or,\,78 \times 750 + 34x = 30 \times 2630 \cr & or,\,34x = 78900 - 58500 \cr & or,\,x = \frac{{20400}}{{34}} \cr & {\text{Hence}},\,x = 600 \cr} $$

Given,
220% of X = 44
Or, X = 20
Thus,
44% of 20
$$ = \frac{{44 \times 20}}{{100}} = 8.8$$

20 litres juice contain 10% Tomato, i.e.
20L juice = $$\frac{{20 \times 10}}{{100}}$$  = 2L Tomato
Tomato puree contains 80% of water and 20% tomato.
This 80% tomato = 2L (which is contained by 100 puree)
So, Now this 2 L Consist 80% in puree
Thus, total puree will be $$\frac{2}{{.8}} = 2.5{\text{L}}$$

Let initial expenses on Sugar was Rs. 100.
Now, Price of Sugar rises 25%. So, to buy same amount of Sugar, y need to expense,
= (100 + 25% of 100) = Rs. 125.
But, They want to keep expenses on Sugar, so y have to cut Rs. 25 in expenses to keep it to Rs. 100.
Now, % decrease in Consumption,
$$\frac{{25}}{{125}} \times 100 = 20\% $$

Mind Calculation Method;
100 === 25%↑ ===> → 125 === X%↓ ===> 100
Here, X = $$\frac{{25}}{{125}} \times 100 = 20\% $$