Mathmetics

ISBT Mathmetics for all banking PO,Clerk,IBPS PO,Railway,SSC,IAS,OAS Exams

Q71.
The sum of two numbers is 28 and their difference is 4. What is the product of the two numbers ?
1) 184 2) 192
3) 196 4) 212
5)None of these
Answer : 192
Explanation :
(x + y)2 = (x - y)2  + 4xy
or x + y = 28, x - y = 4
or 4xy = (28)2 - (4)2
or 4xy = (28 + 4) (28 - 4)
or xy =  = 32 x 6 = 192
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Q72.
A,B and C have to distribute Rs.1200 among themselves. A and C together have Rs. 700 and B and C have Rs.800. How much amount does C have ?
1) Rs.400 2) Rs.500
3) Rs.600 4) Rs.300
5)None of these
Answer : Rs.300
Explanation :
Given, A + B + C = 1200
or A + B + 2C = 700 + 800 = 1500
or 1200 - C + 2C = 1500
or C = 1500 - 1200 = 300
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Q73.
A man spends 1/3rd of his salary on food  and 2/5th on house rent. Then he saves an amount of Rs. 2000 per month. What is his monthly salary ?
1) Rs.6500 2) Rs. 7500
3) Rs.9000 4) Rs.12000
5)None of these
Answer : Rs. 7500
Explanation : Let, the man's income be Rs.x.
Expenditure on food = x/3 and expenditure on house rent = 2x/5
His saving = x - (x/3 + 2x/5) = 4x/15
So,4x/15 = 2000
or x =( 2000 X 15 ) /4 = 7500.
 
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Q74.
The ratio between the present ages of A and B is 2 : 3 respectively. Four years ago, the ratio between their ages was 5 : 8. respectively. What will be A’s age after 7 years ?
1) 29 yrs 2) 35 yrs
3) 31 yrs 4) 33 yrs
5)None of these
Answer : 31 yrs
Explanation :
Let, the present ages of A and B be 2x years and 3x years respectively.
So, (2x-4)/(3x-4) = 5/8
or 16x - 32 = 15x -20 
or  x = 12
Therefore, the Ages of A after 7 years = 2x + 7 = 2 x 12 + 7 = 31 years

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Q75.
Three men or eight boys can do a piece of work in 17 days. How many days will two men and six boys together take to finish the same work ?
1) 9 days 2) 11 days
3) 14 days 4) 12 days
5)None of these
Answer : 12 days
Explanation :
3 men = 8 boys
2 m = (8/3)x2 =  16/3 boys.
(2 men + 6 boys) = (16/2)+6 boys =  34/3boys
8 boys can complete the work in 17 days
or 34/3boys boys can complete the work in x days
or (34/3) : 8 = 17 : x
or x =(17x8x3)/34  = 12 days
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Q76.
Three- tenth of a number is equal to 36% of another number. If the sum of these two numbers is 88, then what is the value of the smaller number ?
1) 38 2) 40
3) 48 4) 56
5)None of these
Answer : 40
Explanation :
Let, one number be x.
The other number = (88 - x)
                x x 3/10 = (88 - x) x 36/100
= 30x = 3168 - 36x
x = 3168/66 = 48
The smaller number = 88 - 48 = 40
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Q77.
If the total cost of four tube-lights and three bulbs is Rs. 260 and the ratio between the cost of a  tube-lights and a bulb is 5 : 2 respectively. What is the total cost one tube-light and six bulbs ?
1) Rs. 210 2) Rs. 130
3) Rs. 180 4) Rs. 170
5)None of these
Answer : Rs. 170
Explanation :
Let, the C.P. of 1 tube light be Rs.5x
C.P. of 1 bulb = Rs. 2x
4 x 5x + 3 x 2x = 260
x = 260/26 = 10
C.P. of 1 tube light and 6 bulbs 
= 5 x X + 6 x 2 xX
= 5 x 10 + 12 x 10 = Rs.170
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Q78.
Alok spends 23% of an amount of money on an insurance policy, 33% on food, 19% of children’s education and 16% on recreation. He deposits the remaining amount of Rs. 504 in bank. How much total amount did he spend on food and insurance policy together ?
1) Rs.3200 2) Rs.3126
3) Rs.3136 4) Rs.3048
5)None of these
Answer : Rs.3136
Explanation :
Let, the total amount of money with Alok be Rs.x .
x = (504 x 100)/[100 - (23+33+19+16) ]= Rs. 5600
Reqd. amount of money
= ( Rs. 5600 x 56)/100= Rs. 3136
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Q79.
The sum of the present ages of Ram, Shyam and Vijay is 72 years. Also the sum of present ages of Ram and Shyam is 42 years. What is the present age of Vijay ?
1) 30 yrs 2) 24 yrs
3) 18 yrs 4) 36 yrs
5)None of these
Answer : 30 yrs
Explanation : The present age of Vijay = 72 - 42 = 30 years
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Q80.
A some of money at compound interest amounts to thrice itself in three years. In how man years will it be nine times itself ? 
1) 4 years 2) 6 years
3) 8 years 4) 12 years
5)None of these
Answer : None of these
Explanation : Let, principal be x.It will be 3x after  years.
9x will takes another 3 years.
So,total time taken= 3+3 = 6 years.


Short-cut method:

x     ------  3x in 3 years 
9x i.e. (3x)2   = 3 X 2 = 6 years. 
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