Aptitude

Question:
What is the unit digit in the product (365 x 659 x 771)?

[A].

1

[B].

2

[C].

4

[D].

6

Answer: Option C

Explanation:

Unit digit in 34 = 1 Unit digit in (34)16 = 1

Unit digit in 365 = Unit digit in [ (34)16 x 3 ] = (1 x 3) = 3

Unit digit in 659 = 6

Unit digit in 74 Unit digit in (74)17 is 1.

Unit digit in 771 = Unit digit in [(74)17 x 73] = (1 x 3) = 3

Required digit = Unit digit in (3 x 6 x 3) = 4.

Question: If x and y are the two digits of the number 653xy such that this number is divisible by 80, then x + y = ?
[A].

2 or 6

[B].

4

[C].

4 or 8

[D].

8

Answer: Option A

Explanation:

80 = 2 x 5 x 8

Since 653xy is divisible by 2 and 5 both, so y = 0.

Now, 653x is divisible by 8, so 13x should be divisible by 8.

This happens when x = 6.

x + y = (6 + 0) = 6.

Question: If the number 42573 * is exactly divisible by 72, then the minimum value of * is:

[A].

4

[B].

5

[C].

6

[D].

7

Answer: Option C

Explanation:

72 = 9 x8, where 9 and 8 are co-prime.

The minimum value of x for which 73x for which 73x is divisible by 8 is, x = 6.

Sum of digits in 425736 = (4 + 2 + 5 + 7 + 3 + 6) = 27, which is divisible by 9.

Required value of * is 6.

Question:
Which one of the following numbers is completely divisible by 99?

[A].

3572404

[B].

135792

[C].

913464

[D].

114345

Answer: Option D

Explanation:

99 = 11 x 9, where 11 and 9 are co-prime.

By hit and trial, we find that 114345 is divisibleby 11 as well as 9. So, it is divisible by 99.

Question: Which one of the following numbers is completely divisible by 45?

[A].

181560

[B].

331145

[C].

202860

[D].

2033555

Answer: Option C

Explanation:

45 = 5 x 9, where 5 and 9 are co-primes.

Unit digit must be 0 or 5 and sum of digits must be divisible by 9.

Among given numbers, such number is 202860.

Question:
If the number 91876 * 2 is completely divisible by 8, then the smallest whole number in place of * will be:

[A].

1

[B].

2

[C].

3

[D].

4

Answer: Option C

Explanation:

Then number 6×2 must be divisible by 8.

   x = 3, as 632 is divisible 8.

Question:
If the number 97215 * 6 is completely divisible by 11, then the smallest whole number in place of * will be:

[A].

3

[B].

2

[C].

1

[D].

5

Answer: Option A

Explanation:

Given number = 97215×6

(6 + 5 + 2 + 9) – (x + 1 + 7) = (14 – x), which must be divisible by 11.

  x = 3

Question:
If the number 481 * 673 is completely divisible by 9, then the smallest whole number in place of * will be:

[A].

2

[B].

5

[C].

6

[D].

7

Answer: Option D

Explanation:

Sum of digits = (4 + 8 + 1 + x + 6 + 7 + 3) = (29 + x), which must be divisible by 9.

   x = 7.

Question: If the number 517*324 is completely divisible by 3, then the smallest whole number in the place of * will be:
[A].

0 

[B].

1

[C].

2

[D].

None of these

Answer: Option C

Explanation:

Sum of digits = (5 + 1 + 7 + x + 3 + 2 + 4) = (22 + x), which must be divisible by 3.

  x = 2.

Question:
What is the unit digit in 7105 ?

[A].

1

[B].

5

[C].

7

[D].

9

Answer: Option C

Explanation:

Unit digit in 7105 = Unit digit in [ (74)26 x 7 ]

But, unit digit in (74)26 = 1

Unit digit in 7105 = (1 x 7) = 7