If the height of a cylinder is increased by 15% and the radius of its base is decreased by 10% then the percentage change in its curved surface area is :
(A) 2.5% increased
(B) 3.5% increased
(C) 2.5% decreased
(D) 3.5% decreased
Solution:
Increase in height = 15% = $$\frac{3}{20}$$ Decrease in base radius = 10% = $$\frac{1}{10}$$ Initial Final Radius 10 9 height 20 23 Area 200 207 Increment in Area = 207 - 200 = 7 Required % increase in area = $$\frac{7}{200}$$ × 100 = 3.5%
572.
In an election between two candidates, 65% of the voters cast their votes, out of which 3% of the votes were decided to be invalid. A candidate got 81965 votes which are 65% of the total valid votes. What is the total number of votes enrolled in that election?
One-eighth of a number is 41.5. What will 69% of that number be ?
(A) 219.12
(B) 225.76
(C) 229.08
(D) 232.4
Solution:
Let the number be x Then, $$\eqalign{ & \Rightarrow \frac{1}{8}x = 41.5 \cr & \Rightarrow x = 41.5 \times 8 \cr & \Rightarrow x = 332 \cr & \therefore 69\% \,\,{\text{of}}\,\,332 \cr & = \left( {\frac{{69}}{{100}} \times 332} \right) \cr & = 229.08 \cr} $$
574.
A's salary was decreased by 50% and subsequently increased by 50%. How much percent does he lose ?
(A) 25%
(B) 30%
(C) 20%
(D) No loss
Solution:
Let A salary's in starting is = 100 Now after decreased by 50% A salary become = 50 Again 50% of salary increase i.e. 50% of 50 = 25 Current salary is = 50 + 25 = 75 Actual decrease in salary of A = 100 - 75 = 25 Actual % lose = $$\frac{25}{100}$$ × 100 = 25%
575.
If the sum of 40% of a number and 30% of the same number is 70, then the number is:
(A) 125
(B) 100
(C) 150
(D) 200
Solution:
Let, number = x 40% of x + 30% of x = 70 70% of x = 70 x = 100
576.
If x% of y is the same as $$\frac{4}{5}$$ of 80, then the value of xy is :
Rishu saves x% of her income. If her income increases by 26% and the expenditure increases by 20%. then her savings increase by 50%. What is the value of x?
If the price of a commodity is decreased by 20% and its consumption is increased by 20%, what will be the increase or decrease in expenditure on the commodity?
(A) 4% increase
(B) 4% decrease
(C) 8% increase
(D) 8% decrease
Solution:
Let the initial expenditure on the commodity be Rs. 100. Now, the price decreases by 20%, Current Price = (100 - 20% of 100) = Rs. 80. Same time due to decrements in price 20% consumption has been increased. So, Current expenses on commodity = (80 + 20% of 80)= Rs. 96. Here, the initial expenditure was Rs. 100 which became 96 at the end, it means there is 4% decrements in the expenditure of the commodity. Mind Calculation Method: 100 === 20%↓(Decrements in Price) ===> 80 === 20%↑(Increment in Consumption) ===> 96. Thus, there is a decrements of 4%
580.
A man spend $$7\frac{1}{2}$$% of his money and after spending 75% of the remaining he had Rs. 370 left. How much money did he have :
(A) 1200
(B) 1600
(C) 1500
(D) 1400
Solution:
Let the 100unit is the salary of the person After spending 7.5% of his salary remain salary 92.5 Now again he spended 75% of 92.5 and remain 25% which have value Rs. 370 According to the question, 92.5 × 25% unit = 370 92.5 × $$\frac{1}{4}$$ unit = 370 1 unit = $$\frac{370 × 4}{92.5}$$ 100 unit = $$\frac{370 × 4 × 100}{92.5}$$ = Rs. 1600