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91
The population of a town is 4.2 × 106. If the population increases by 75 per 1000 per annum, then what will be the population after 2 years ?
Discuss
Answer & Solution
Answer: Option B
Solution:
Percentage annual increase :
$$\eqalign{ & = \left( {\frac{{75}}{{1000}} \times 100} \right)\% \cr & = 7\frac{1}{2}\% \cr & = \frac{{15}}{2}\% \cr} $$
Population after 2 years :
$$\eqalign{ & = 4200000{\left( {1 + \frac{{15}}{{2 \times 100}}} \right)^2} \cr & = \left( {4200000 \times \frac{{43}}{{40}} \times \frac{{43}}{{40}}} \right) \cr & = 4853625 \cr} $$
92
A's marks in Biology are 20 less than 25% of the total marks obtained by him in Biology, Maths and Drawing. If his marks in Drawings be 50, what are his marks in Maths ?
Discuss
Answer & Solution
Answer: Option D
Solution:
Let B + M + D = $$x$$
Then,
B = 25 of $$x$$ - 20
$$\eqalign{ & = \left( {\frac{{25x}}{{100}} - 20} \right) \cr & = \left( {\frac{x}{4} - 20} \right) \cr} $$
And D = 50
∴ $$\frac{x}{4}$$ - 20 + M + 50 = $$x$$
or M = $$\left( {\frac{{3x}}{{4}} - 30} \right)$$
So, marks in Maths cannot be determined.
93
If x = 63% of y, then y2 is approximately what percent of x2 ?
Discuss
Answer & Solution
Answer: Option C
Solution:
x = 63% of y
⇒ x = $$\frac{63y}{100}$$
⇒ y = $$\frac{100x}{63}$$
∴ Required percentage :
$$\eqalign{ & = \left( {\frac{{{y^2}}}{{{x^2}}} \times 100} \right)\% \cr & = \left[ {{{\left( {\frac{{100x}}{{63}}} \right)}^2} \times \frac{1}{{{x^2}}} \times 100} \right]\% \cr & = \left( {\frac{{10000}}{{3969}} \times 100} \right)\% \cr & = 251.96\% \approx 250\% \cr} $$
94
A number is first decreased by 10% and then increased by 10%. The number so obtained is 50 less than the original number. The original number is :
Discuss
Answer & Solution
Answer: Option A
Solution:
Let the original number be $$x$$
Final number obtained :
= 110% of (90% of $$x$$)
= $$\left( {\frac{{110}}{{100}} \times \frac{{90}}{{100}} \times x} \right)$$
= $$\frac{{99x}}{{100}}$$
$$\eqalign{ & \therefore x - \frac{{99x}}{{100}} = 50 \cr & \Rightarrow \frac{x}{{100}} = 50 \cr & \Rightarrow x = 50 \times 100 \cr & \Rightarrow x = 5000 \cr} $$
95
A city has a population of 300000 out of which 180000 are males. 50% of the population is literate. If 70% of the males are literate, then the percentage of female who are literate is :
Discuss
Answer & Solution
Answer: Option A
Solution:
Number of males = 180000
Number of females :
= (300000 - 180000)
= 120000
Number of literates :
= 50% of 300000
= 150000
Number of literate males :
= 70% of 180000
= 126000
Number of literate females :
= (150000 - 126000)
= 24000
∴ Required percentage :
= $$\left( {\frac{{24000}}{{120000}} \times 100} \right)\% $$
= 20%
96
The price of an articles was increased by r%. Later the new price was decreased by r%. If the latest price was Rs. 1, then the original price was :
Discuss
Answer & Solution
Answer: Option D
Solution:
Let the original price be Rs. $$x$$
∴ (100 - r)% of (100 + r)% of $$x$$ = 1
$$\eqalign{ & \Rightarrow \frac{{\left( {100 - r} \right)}}{{100}} \times \frac{{\left( {100 + r} \right)}}{{100}} \times x \cr & \Rightarrow x = \frac{{100 \times 100}}{{\left( {100 - r} \right)\left( {100 + r} \right)}} \cr & \Rightarrow x = \frac{{10000}}{{\left( {10000 - {r^2}} \right)}} \cr} $$
97
In September 2009, the sales of a product were $$\frac{2}{3}$$rd of the that in July 2009. In November 2009, the sales of the product were higher by 5% as compared to September 2009. How much is the percentage of increase on sales in November 2009 with respect to the base figure in July 2009 ?
Discuss
Answer & Solution
Answer: Option C
Solution:
Let the total sales in July 2009 be Rs. $$x$$
Then, sales in September 2009 = Rs. $$\frac{2x}{3}$$
Sales in November 2009 :
= 105% of Rs. $$\frac{2x}{3}$$
= Rs. $$\left( {\frac{{105}}{{100}} \times \frac{{2x}}{3}} \right)$$
= Rs. $$\frac{7x}{10}$$
Decrease in sales :
= Rs. $$\left( {x - \frac{{7x}}{{10}}} \right)$$
. = Rs. $$\frac{3x}{10}$$
∴ Decrease % :
= $$\left( {\frac{{3x}}{{10}} \times \frac{1}{x} \times 100} \right)\% $$
= 30%
98
Two numbers are respectively 25% and 60% more than a third number. The ratio of the two numbers is:
Discuss
Answer & Solution
Answer: Option C
Solution:
\[\begin{array}{*{20}{c}} {\text{I}}&{}&{{\text{II}}}&{{\text{III}}} \\ {125}&:&{160}&{100} \\ {25}&:&{32}&{} \end{array}\]
99
The income of A is 80% of B's income and the expenditure of A is 60% of B's expenditure. If the income of A is equal to 90% of B's expenditure, then by what percentage are the saving of A more than B's savings?
Discuss
Answer & Solution
Answer: Option A
Solution:
Income of A is 80% of B
$$\eqalign{ & A = B \times \frac{{80}}{{100}} \cr & \frac{A}{B} = \frac{{4x}}{{5x}} \cr} $$
Expenditure of A is 60% of expenditure of B
$$\eqalign{ & A = B \times \frac{{60}}{{100}} \cr & \frac{A}{B} = \frac{{3y}}{{5y}} \cr} $$
Income of A is 90% of income of B
$$\eqalign{ & 4x = \frac{{90}}{{100}} \times 5y \cr & 8x = 9y \cr & \frac{x}{y} = \frac{9}{8} \cr} $$
Saving ratio of A and B
= (4x - 3y) : (5x - 5y)   [∴ 8x = 9y]
= (4 × 9 - 3 × 8) : (5 × 9 - 5 × 8)
= (36 - 24) : (45 - 40)
= 12 : 5
More = 12 - 5 = 7
More% $$ = \frac{7}{5} \times 100 = 140\% $$

Alternate solution
\[\begin{array}{*{20}{c}} {}&{{\text{A}}\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,{\text{B}}} \\ {{\text{Income}} \to }&{4 \times 5 \times 9 = 180\,\,\,\,\,\,\,\,\,\,5 \times 5 \times 9 = 225} \\ {{\text{Expenditure}} \to }&{3 \times 4 \times 10 = 120\,\,\,\,\,\,\,\,\,\,5 \times 4 \times 10 = 200} \\ {{\text{Saving}} \to }&{\overline {\underline {\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,60\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,:\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,25\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,} } } \end{array}\]
Ratio of A saving to B saving = 60 : 25 = 12 : 5
More = 12 - 5 = 7
More% $$ = \frac{7}{5} \times 100 = 140\% $$
100
What is to be added to 15% of 180 so that the sum is equal to 20% of 360?
Discuss
Answer & Solution
Answer: Option A
Solution:
$$\eqalign{ & {\text{Let be the number is }}x \cr & 180 \times \frac{{15}}{{100}} + x = \frac{{360 \times 20}}{{100}} \cr & 27 + x = 72 \cr & x = 72 - 27 \cr & x = 45 \cr} $$