If the number 357*25* is divisible by both 3 and 5, then the missing digits in the unit's place and the thousandth's place respectively are :
SOLUTION ANALYSIS
Correct Option: D
Let the unit's place be x and the thousand's place be y.
Then, 357y25x is divisible by 5 only when x = 0 or x = 5
Also, this number is divisible by 3 only when sum of its digits is divisible by 3
So, (22 + x + y) must be divisible by 3
∴ x + y = 2
Taking x = 0, we get y = 2
So, the unit place = 0 and thousand's place = 2
Question 2 of 20
Hint
The number of times 99 is subtracted from 1111 so that the remainder is less then 99 is :
SOLUTION ANALYSIS
Correct Option: B
On dividing 1111 by 99, the quotient is 11 and the remainder is 22.
Hence, the required number is 11
Question 3 of 20
Hint
Two numbers when divided by a certain divisor leave the remainders 4375 and 2986 respectively but when the sum of two numbers is divided by the same divisor, the remainder is 2361. The divisor in question is :
SOLUTION ANALYSIS
Correct Option: C
As proved in the above question,
Divisor = 4375 + 2986 - 2361
= 5000
Question 4 of 20
Hint
If a + b + c = 0, (a + b) (b + c) (c + a) equals
SOLUTION ANALYSIS
Correct Option: C
a + b + c = 0 ⇒ (a + b) = - c
(b + c) = - a and (c + a) = - b
⇒ (a + b) (b + c) (c + a)
= (- c) × (- a) × (- b)
= - (abc)
Question 5 of 20
Hint
If m = - 4, n = - 2, then the value of m3 - 3m2 + 3m + 3n + 3n2 + n3 is :
(xn + an) is divisible by (x + a) when n is odd
∴ (2525 + 125) is divisible by (25 + 1)
⇒ (2525 + 1) is divisible by 26
⇒ On dividing 2525 by 26, we get (26 - 1) = 25 as remainder
Question 7 of 20
Hint
The smallest three-digit prime number is :
SOLUTION ANALYSIS
Correct Option: A
Clearly, 100 is divisible by 2. So, 100 is not prime.
(101) < (11)2 and prime numbers less than 11 are 2, 3, 5, 7
Clearly, 101 is not divisible by any of 2, 3, 5 and 7
Hence, 101 is the smallest 3-digit prime number.
p < 1
⇒ $$\frac{1}{p}$$ > 1
⇒ $$\frac{2}{p}$$ > 2
⇒ $$\frac{2}{p}$$ - p > 2 - p > 0 [∵ p < 1]
Hence, $$\left( {\frac{2}{p} - p} \right)$$ is a positive number
Question 10 of 20
Hint
(xn - an) is divisible by (x - a)
SOLUTION ANALYSIS
Correct Option: A
We know that (xn - an ) is always divisible by (x - a) for all values of n.
Question 11 of 20
Hint
How many prime numbers are there between 100 to 200 ?
SOLUTION ANALYSIS
Correct Option: A
The number of prime numbers from 100 to 200 is 21.
If x is a rational number and y is an irrational number, then-
SOLUTION ANALYSIS
Correct Option: D
(a) Let x = 0 and y = $$\sqrt 2 $$
Then, x is rational and y is irrational.
∴ x + y = 0 + $$\sqrt 2 $$ = $$\sqrt 2 $$ , which is irrational
Thus, x + y is not rational
(b) Let x = 0 and y = $$\sqrt 2 $$
Then, x is rational and y is irrational
∴ xy = 0 × $$\sqrt 2 $$ = 0, which is rational
Hence, xy is not irrational
(c) As shown in (B), xy is not necessarily irrational
(d) x + y is necessary irrational. But xy can be either rational or irrational.
Hence, (D) is true.
Question 13 of 20
Hint
If a and b are positive integers and $$\frac{(a - b)}{3.5}$$ = $$\frac{4}{7}$$, then:
SOLUTION ANALYSIS
Correct Option: B
$$\frac{(a - b)}{3.5}$$ = $$\frac{4}{7}$$
⇒ (a - b) = $$\frac{4}{7}$$ × $$\frac{7}{2}$$ = 2
⇒ b < a
Question 14 of 20
Hint
The digits indicated by * in 3422213** so that this number is divisible by 99 are :
SOLUTION ANALYSIS
Correct Option: A
Let the unit's digit be x and ten's digit be y
Then, the number is 3422213yx
Also, 99 = (11 × 9), where 11 and 9 are co-primes
Since the given number is divisible by 9, it follows that (3 + 4 + 2 + 2 + 2 + 1 + 3 + y + x) = (17 + y + x) must be divisible by 9
So, y + x = 1 or y + x = 10
Again, the given number is divisible by 11
So, (x + 3 + 2 + 2 + 3) - (y + 1 + 2 + 4) = x - y + 3 is either 0 or 11
∴ (x - y + 3 = 0 or x - y + 3 = 11)
⇒ (y - x = 3 or x - y = 8)
Now, (y + x = 1 and y - x = 3)
⇒ y = 2 and x = - 1
(y + x = 1 and x - y = 8)
⇒ x = $$\frac{9}{2}$$
(y + x = 10 and y - x = 3)
⇒ y = $$\frac{13}{2}$$
(y + x = 10 and x - y = 8)
⇒ x = 9 and y = 1
Thus, x = 9, y = 1
So, required number is 342221319
Question 15 of 20
Hint
(46351 - 36418 - 4505) ÷ ? = 1357
SOLUTION ANALYSIS
Correct Option: C
Let $$\frac{46351 - 36418 - 4505}{x}$$ = 1357
Then,
x = $$\frac{46351 - (36418 - 4505)}{1357}$$
x = $$\frac{(46351 - 40923)}{1357}$$
x = $$\frac{5428}{1357}$$
x = 4
Question 16 of 20
Hint
Given that (12 + 22 + 32 + ..... + 202) = 2870, the value of (22 + 42 + 62 + ... + 402 ) is :
The digit in the unit's place of [(251)98 + (21)29 - (106)100 + (705)35 - 164 + 259] is :
SOLUTION ANALYSIS
Correct Option: B
Unit digit in [(251)98 + (21)29 - (106)100 + (705)35 - 164 + 259]
= unit digit in (1 + 1 - 6 + 5 - 6 + 9)
= 4
Question 20 of 20
Hint
Which of the following numbers is exactly divisible by 24 ?
SOLUTION ANALYSIS
Correct Option: D
We have 24 = 3 × 8, where 3 and 8 are co-primes
Clearly,
718 is not divisible by 8. So, 35718 is not divisible by 8
810 is not divisible by 8. So, 63810 is not divisible by 8
804 is not divisible by 8. So, 537804 is not divisible by 8
736 is divisible by 8. So, 3125736 is divisible by 8
Also, sum of its digits = (3 + 1 + 2 + 5 + 7 + 3 + 6) = 27, which is divisible by 3
So, 3125736 is divisible by 3 also.
Hence, it is divisible by 24.