Playing With Numbers(8th Grade > Mathematics ) Questions and answers for exam Preparation

8th Grade > Mathematics

PLAYING WITH NUMBERS MCQs

Total Questions : 54 | Page 2 of 6 pages

Question 11. Which of the following is not divisible by 2?

123123
34567896
2345678234
18322

Discuss Question

Answer: Option A. -> 123123
:
A
All the even numbers and the numbers ending with 0 are divisible by 2.
Among the given options,123123 has its last digit as 3 which makes it an odd number.Hence, this number is not divisible by 2.

Question 12.

1000 \times 2 + 100 \times 3 + 10 \times 2 + 1 \times 4

is expressed as:

4232
1111
2024
2324

Discuss Question

Answer: Option D. -> 2324
:
D

1000 \times 2 + 100 \times 3 + 10 \times 2 + 1 \times 4 = 2000 + 300 + 20 + 4 = 2324

Question 13. Soham got a call from Manish who was not very clear with the concepts of divisibility. Manish then asked, "Is 244 divisible by 2?” . Soham replied yes. Is Soham's reply true or false?

True
False
8
6

Discuss Question

Answer: Option A. -> True
:
A
Ifthe ones digit of a number is 0, 2, 4, 6 or 8 then the number is divisible by 2.
For the number 244 in the ones place we find 4 which is divisible by 2. Therefore we can say that the number 244 is divisible by 2.

Question 14. When Rashi ordered pizza and coke, the bill had the digits A and B not visible clearly.

\begin{matrix} P i z z a A & 1 & 2 C o k e + 3 & 1 & B 5 & 2 & 5 \end{matrix}

Using the information visible on her bill, find the digits A and B respectively.

A = 2, B = 1
A = 3, B = 5
A = 1, B = 3
A = 2, B = 3

Discuss Question

Answer: Option D. -> A = 2, B = 3
:
D
In the tens place, the numbers being added are 1 and 1. The sum given in the tens place is2, which means there is no carry over throughout the summation.
A + 3 = 5 i.e A = 5 - 3 = 2 and
2 + B = 5 i.e B = 5 - 2 = 3

\begin{matrix} P i z z a 2 & 1 & 2 C o k e + 3 & 1 & 3 5 & 2 & 5 \end{matrix}

Question 15. Find Q in the addition

\begin{matrix} 31 Q + 1 Q 3 501 \end{matrix}

Discuss Question

Answer: Option D. -> 8
:
D
Study the addition in the ones column:
Q + 3 = 1,a number whose ones digit is 1.
If Q = 8, then 8 + 3 = 11.
So, the puzzle can be solved as shown below:

\begin{matrix} 318 + 183 501 \end{matrix}

Hence, Q = 8

Question 16. Soham borrowed money from his mother for buying pens. He bought 7 pens and the price of each pen is a two digit number, 1A. If the total amount spent by him is 10A, then the value of A is
___

Discuss Question

:
Price of one Pen

= 1 \times 10 + A

Number of Pens = 7
Total price

= (10 + A) \times 7

(10 + A) \times 7 = (100 + A)

70 + 7A = 100 + A
6A = 30
A = 5

Question 17. Aarush asked Soham to take any 2 or 3 digit number and reverse the digits, then subtract the larger number from the smaller number. Soham did the same and concluded that the result is exactly divisible by 9. What Soham concluded is:

True
False
2024
2324

Discuss Question

Answer: Option A. -> True
:
A
Let's considera two digitnumber ab.Its general form will be

10 \times a + 1 \times b

.
If wereverse the digits, its general form will be

10 \times b + 1 \times a

. If we subtract both of the numbers, we get:

(10 \times a + 1 \times b) - (10 \times b + 1 \times a)

= (10a + b) - (10b + a)
= 10a + b -10b - a
= 9a - 9b
= 9 (a-b)
Observe that the result is a multiple of 9 and hence is exactly divisible by 9.
Similarly, for 3 digit numbers, the difference of the number and number obtained by reversing the digits (if abc is the number) will be given by:

(100 \times a + 10 \times b + c) - (100 \times c + 10 \times b + a)

=100a + 10b + c - (100c + 10b + a)
= 100a + 10b + c - 100c - 10b - a
= 99a - 99c
= 99 (a-c)
=

9 \times 11 (a - c)

which is also divisible by 9.
Note that this happens with any 2 or 3number.

Question 18. I take a 3 digit number with distinct digits. I can get 6 different 3 digit numbers by rearranging the digits of this number.

True
False
50
51

Discuss Question

Answer: Option A. -> True
:
A
Let the3 digit number beabc.On rearrangingthedigits I get, abc, bac, cba, cab, acb, bca. Hence Iwill get 6 three digit numbers.

Question 19. What is the remainder when 1591 is divided by 1000?

Discuss Question

Answer: Option C. -> 591
:
C
On dividing 1591 by 1000, the remainder is the last 3 digits. Hence it is 591.

Question 20. (f × 100) + (d × 10) + e is written as

Discuss Question

Answer: Option C. -> fde
:
C
(f×100) + (d×10) + e is written asfde which is a three digit number.
For example, (2