Number System
1. The difference between a two-digit number and the number obtained by interchanging the digits is 36. What is the difference between the sum and the difference of the digits of the number if the ratio between the digits of the number is 1 : 2?
A. 4
B. 8
C. 16
D. None of these
Answer: Option (B)
Explanation:
Since the number is greater than the number obtained on reversing the digits, so the ten's digit is greater than the unit's digit.
Let ten's and unit's digits are 2x and x respectively.
Then, (10 x 2x + x) - (10x + 2x) = 36
9x = 36
x = 4.
Required difference = (2x + x) - (2x - x) = 2x = 8.
2. The difference between a two-digit number and the number obtained by interchanging the positions of its digits is 36. What is the difference between the two digits of that number?
A. 3
B. 4
C. 9
D. Cannot be determined
E. None of these
Answer: Option (B)
Explanation:
Let the ten's digit be x and unit's digit be y.
Then, (10x + y) - (10y + x) = 36
9(x - y) = 36
x - y = 4.
3. Three times the first of three consecutive odd integers is 3 more than twice the third. The third integer is:
Answer: Option (D)
Explanation:
Let the three integers be x, x + 2 and x + 4.
Then, 3x = 2(x + 4) + 3
x = 11.
Third integer = x + 4 = 15.
4. A number consists of two digits. If the digits interchange places and the new number is added to the original number, then the resulting number will be divisible by:
Answer: Option (D)
Explanation:
Let the ten's digit be x and unit's digit be y.
Then, number = 10x + y.
The number obtained by interchanging the digits = 10y + x.
(10x + y) + (10y + x) = 11(x + y), which is divisible by 11.
5. A number consists of 3 digits whose sum is 10. The middle digit is equal to the sum of the other two and the number will be increased by 99 if its digits are reversed. The number is:
A. 145
B. 253
C. 370
D. 352
Answer: Option (B)
Explanation:
Let the middle digit be x.
Then, 2x = 10 or x = 5. So, the number is either 253 or 352.
Since the number increases on reversing the digits, so the hundred's digits are smaller than the unit's digit.
Hence, the required number = 253.
Decimals
1. 3 x 0.3 x 0.03 x 0.003 x 30 =?
A. 0.0000243
B. 0.000243
C. 0.00243
D. 0.0243
Answer: Option (C)
Explanation:
3 x 3 x 3 x 3 x 30 = 2430. Sum of decimal places = 6
Therefore, 3 x 0.3 x 0.03 x 0.003 x 30 = 0.002430 = 0.00243
2. A tailor has 37.5 meters of cloth and he has to make 8 pieces out of a meter of cloth. How many pieces can he make out this cloth?
A. 300
B. 360
C. 400
D. 450
Answer: Option (A)
Explanation:
Length of each piece = (1/8) m = 0.125 m
Required no of pieces = (37.5/0.125) = (375 * 100) / 125 = 300.
3. The price of commodity X increases by 40 paise every year, while the price of commodity Y increases by 15 paise every year. If in 2001, the price of commodity X was Rs. 4.20 and that of Y was Rs. 6.30, in which year commodity X will cost 40 paise more than the commodity?
A. 2010
B. 2011
C. 2012
D. 2013
Answer: Option (B)
Explanation:
Suppose commodity X wil cost 40 paise more than Y after Z years. Then,
(4.20 + 0.40Z) - (6.30 + 0.15Z) = 0.40
=> 0.25Z = 0.40 + 2.10 => Z= 2.50/0.25 = 10
Therefore, X will cost 40 paise more than Y 10 years after 2001. i.e in 2011.
4. What is the difference between the biggest and the smallest fraction among 2/3, 3/4, 4/5 and 5/6?
A. 1/6
B. 1/12
C. 1/20
D. 1/30
Answer: Option (A)
Explanation:
Converting each of the given fractions into decimal form, we get
2/3 = 0.66, 3/4 = 0.75, 4/5 = 0.8, 5/6 = 0.833
Since 0.833>0.8>0.75>0.66
So, 5/6 > 4/5 > 3/4 > 2/3
Therefore, Required Difference = 5/6 - 2/3 = 1/6.
5. 54.327 x 357.2 x 0.0057 is same as
A. 5.4327 x 3.572 x5.7
B. 5.4327 x 3.572 x0.57
C. 54327 x 3572 x 0.0000057
D. None of these
Answer: Option (A)
Explanation:
Number of decimal places in the given expression = 8
Number of decimal places in (A) = 8
Number of decimal places in (B) = 9
Number of decimal places in (C)= 7
Clearly, the expression in (A) is the same as the given Expression.
Fractions
1. 0.004 × 0.5 = ?
A. None of these
B. 0.02
C. 0.002
D. 0.0002
Answer: Option (C)
Explanation:
0.004 × 0.5 = 0.002
2. How many digits will be there to the right of the decimal point in the product of 89.635 and .02218?
Answer: Option (C)
Explanation:
Sum of decimal places = 3 + 5 = 8
The last digit in the product(digit at the extreme right) is zero (Since 5 x 8 = 40)
Hence, there will be 7 significant digits to the right of the decimal point.
3. 24.39 + 562.093 + 35.96 = ?
A. 622.441
B. 622.243
C. 622.233
D. 622.443
Answer: Option (D)
Explanation:
24.39 + 562.093 + 35.96 = 622.443.
4. What decimal of an hour is a second?
A. 0.00027
B. 0.00025
C. 0.00026
D. 0.00024
Answer: Option (A)
Explanation:
1 hour = 60 minutes = 3600 seconds
Hence, required decimal = 1/3600 = 0.00027
5. Which of the following is equal to 0.024 × 10[latex]^{6 }[/latex]?
A. 2400000
B. 240000
C. 24000
D. 2400
Answer: Option (C)
Explanation:
0.024 × 10[latex]^{6 }[/latex] = 0.024 × 1000000 = 24000
LCM
1. Product of two co-prime numbers is 117. Their L.C.M should be
A. 1
B. 117
C. Equal to their H.C.F
D. cannot be calculated
Answer: Option (B)
Explanation:
H.C.F of co-prime numbers is 1. So, L.C.M = 117/1 =117
2. The ratio of two numbers is 3: 4 and their H.C.F is 4. Their L.C.M is
Answer: Option (D)
Explanation:
Let the numbers be 3x and 4x. Then their H.C.F = x. So, x=4
Therefore, The numbers are 12 and 16
L.C.M of 12 and 16 = 48
3. L.C.M of two prime numbers x and y (x>y) is 161. The value of 3y-x is :
Answer: Option (A)
Explanation:
H. C. F of two prime numbers is 1. Product of numbers = 1 x 161 = 161.
Let the numbers be a and b. Then, ab= 161.
Now, co-primes with product 161 are (1, 161) and (7, 23).
Since x and y are prime numbers and x > y, we have x=23 and y=7.
Therefore, 3y-x = (3 x 7)-23 = -2
4. The least number which when divided by 5, 6, 7 and 8 leaves a remainder 3, but when divided by 9 leaves no remainder, is:
A. 1677
B. 1683
C. 2523
D. 3363
Answer: Option (B)
Explanation:
L.C.M. of 5, 6, 7, 8 = 840.
The required number is of form 840k + 3
Least value of k for which (840k + 3) is divisible by 9 is k = 2.
Required number = (840 x 2 + 3) = 1683.
5. If HCF of two numbers is 8, which of the following can never be their LCM?
Answer: Option (C)
Explanation:
60 is not a multiple of 8
HCF
1. The G.C.D of 1.08, 0.36 and 0.9 is
A. 0.03
B. 0.9
C. 0.18
D. 0.108
Answer: Option (C)
Explanation:
Given numbers are 1.08, 0.36 and 0.90
H.C.F of 108, 36 and 90 is 18 [ ∵ G.C.D is nothing but H.C.F]
Therefore, H.C.F of given numbers = 0.18.
2. Three numbers are in the ratio 1: 2: 3 and their H.C.F is 12. The numbers are
A. 4, 8, 12
B. 5, 10, 15
C. 10, 20, 30
D. 12, 24, 36
Answer: Option (D)
Explanation:
Let the required numbers be x, 2x, 3x. Then, their H.C.F =x. so, x= 12
Therefore, The numbers are 12, 24, 36.
3. The maximum number of students among them 1001 pens and 910 pencils can be distributed in such a way that each student gets the same number of pens and the same number of pencils is:
A. 91
B. 910
C. 1001
D. 1911
Answer: Option (A)
Explanation:
Required number of students = H.C.F of 1001 and 910 = 91.
4. Three number are in the ratio of 3: 4: 5 and their L.C.M. is 2400. Their H.C.F. is:
A. 40
B. 80
C. 120
D. 200
Answer: Option (A)
Explanation:
Let the numbers be 3x, 4x and 5x.
Then, their L.C.M. = 60x.
So, 60x = 2400 or x = 40.
The numbers are (3 x 40), (4 x 40) and (5 x 40).
Hence, the required H.C.F. = 40.
5. The greatest number which on dividing 1657 and 2037 leaves remainders 6 and 5 respectively, is:
A. 123
B. 127
C. 235
D. 305
Answer: Option (B)
Explanation:
Required number = H.C.F. of (1657 - 6) and (2037 - 5)
= H.C.F. of 1651 and 2032 = 127.