:
Formula: 1 Mark
Steps: 1 Mark
Answer: 1 Mark
Number of questions Aarush used to solve initially = 4 questions in 16 minutes
Time needed to solve a question = $\frac{16}{4}$ = 4 minutes
Number of questions Aarush can solve after practising = 6 questions in 18 minutes
Time needed to solve a question = $\frac{18}{6}$ = 3 minutes
Decrease in time to solve a single question = 4 - 3 = 1 minutes.
Therefore, the percentage decrease is given by
Decrease Percent = $\frac{\text{amount decreased}}{\text{Original or base}}\times 100$
On substituting the values, weget:
Decrease in percentage = $\frac{1}{4}\times 100$ = 25%
Hence, after practising Aarush reduced 25% of the time to solve a single question.

:
Concept: 1Mark
Steps: 1Mark
Answer: 1 Mark Each
Given that,
Cost price = ₹ 2500
Selling price = ₹ 3000
Selling price > Cost price $\Rightarrow$ Profit
$\therefore$ Profit = 3000 - 2500 = ₹ 500
$\text{Profit}\%=\frac{\text{Profit}}{CP}\times 100$
$\text{Profit}\%=\frac{500}{2500}\times 100$
$\text{Profit}\%=20\%$
Now it was sold for ₹ 2000.
The selling price, SP = ₹ 2000
SP<CP
Therefore it is a case of loss.
Loss = CP - SP = 2500 - 2000 = ₹ 500
So, the loss $\%$ is given by,
Loss$\%$ = $\frac{500}{2500}\times 100$ = 20$\%$

:
Formula: 1 Mark
Steps: 2 Marks
Answer: 1 Mark
Given,
Meena pays an interest of ₹ 45 for one year.
The rate of interest is 9 %
Interest = ₹ 45
Time = 1 year
Rate of interest = 9%
Let the principal be P
We know that,
$S.I=\frac{P\times R\times T}{100}$
$45=\frac{P\times 9\times 1}{100}$
$\Rightarrow P=\frac{45\times 100}{9}$
$\therefore P=$₹500
The sum she borrowed is ₹ 500.
The net amount she will pay at the end of one year = 500 + 45 = ₹ 545.

:
Steps: 1 Mark
Answer: 1 Mark
Given that:
In a city, there are 15000 voters.
60% of the voters voted.
Total percentage of voters = 100%
Voters who voted in % = 60%
$\Rightarrow$ Percentage of voters who did not vote
= 100 - 60 = 40%
Total Voters = 15000
40% of 15000 did not vote.
Then, the number of voters who did not vote is:
= 40% of 15000
$\Rightarrow \frac{40}{100}\times 15000=6000$
$\therefore$ 6000 voters did not vote.

:
Steps: 2 Marks
Answer: 1 Mark each
Given that:
Meet saves ₹ 4000 from her salary, which is 10% of her salary.
Let Meet’s salary be ₹$x$
Given that,
$10\%ofx=4000$
$\frac{10}{100}\times x=4000$
$\frac{x}{10}=4000$
$x=4000\times 10=₹40000$
Therefore, Meet’s salary is ₹ 40,000.
Her net expenditure= Salary - savings = 40000 - 4000 = ₹ 36,000
Now in order to buy a bike Meet starts saving $30\%$ of her salary.
Her salary is ₹ 40,000.
The total amount she starts saving monthly = $\frac{30}{100}\times 40,000$ = $₹12,000$
Her net saving monthly is ₹ 12,000.

:
Calculations: 1Mark
Steps: 1Mark
Answer: 1 Mark
Cost price= ₹12000, overhead charges= ₹2850
$\therefore$ Total cost price = ₹ (12000 + 2850) = 14850
Selling Price = ₹ 13860
Selling Price < Cost Price $\Rightarrow$ Loss
$\therefore$ Loss = Cost price - Selling price
$\Rightarrow$ Loss =₹ (14850-13860) = ₹ 990
Loss percentage = $\frac{Loss}{CostPrice}\times 100$
Loss percentage = $\frac{990}{14850}\times 100$ = 6.7 %
So, Ravi incurred a loss of 6.7%.

:
Formula: 1 Mark
Steps: 1 Mark
Each answer: 1 Mark
Given,
Harish borrowed₹ 7500 from a bank.
a) The rate of interest is 5 % p.a.
The principal amount, P =₹ 7500
Rate of Interest, R = 5 % p.a.
Time, T = 3 years
$S.I.=\frac{P\times R\times T}{100}$
$S.I.=\frac{7500\times 5\times 3}{100}$
S.I.=₹1125
Amount = Principal + Interest
$\Rightarrow$ Amount = 7500 + 1125
Amount = ₹ 8625
Hence, the total amount to be paid at the end of three years is ₹8625
b) Now, Harish was able to pay only ₹5625.
So, the remaining amount
= ₹(8625 - 5625) =₹ 3000
The new principal amount = ₹ 3000
The rate of interest is same =5 % p.a.
The interest which he has to pay at the end of the fourth year
=$\frac{5}{100}\times 3000$ = ₹150
So, the amount which Harish has to pay at the end of the fourth year
= 3000 + 150 = ₹3150

:
For 6 students we need 3 balls.
$\Rightarrow$ For 1 student, we need $\frac{3}{6}=\frac{1}{2}$ balls.
Therefore, 36 students would need:
$36\times \frac{1}{2}=$ 18 balls.

:
Steps: 1Mark
Application: 1Mark
Calculation: 1Mark
Marks scored in the 1st test = 70
Marks scored in the 1st test = 85
Increase in marks = 1st test mark - 2nd test marks
Increase in marks = 85 - 70 = 15
Increase in percentage
$=\left(\frac{Increase}{Originalmarks}\right)\times 100$
Increase in percentage
$=\left(\frac{15}{70}\right)\times 100$ = 21.42 %

:
Concept: 1Mark
Application: 1Mark
Each Answer: 1 Mark
Given that
Amina bought a book for ₹ 275.
So the Cost price, CP = ₹ 275.
$Loss\%=15\%$
$Loss=15\%of275$
$Loss=\frac{15}{100}\times 275$
$Loss=\frac{4125}{100}$
$Loss=41.25$
$Sellingprice=Costprice-Loss$
$Sellingprice=275-41.25$
$Sellingprice=₹233.75$
Hence she sold it at ₹ 233.75.
If she has sold at ₹ 286,
The selling price, SP = ₹ 286
Profit = SP - CP
$\therefore$ On substituting the values we get, Profit = (286 - 275) = ₹ 11
Now, Profit % $=\frac{profit}{CostPrice}\times 100$
Profit % $=\frac{11}{275}\times 100=4$
$\therefore$ Had she sold it at ₹ 286 her profit% would have been 4%.