Quantitative Aptitude

Number System and Digits

374 Questions

Number system and digits questions test the ability to manipulate numbers, identify significant digits, and form specific values. These problems often require finding missing digits or determining the properties of large sums. They form a vital component of the quantitative aptitude section.

Number formationMissing digitsSignificant digitsLargest and smallest numbersDigit sum properties

Number System and Digits Questions

Multiple choice maths equations and simple functions further equations solving linear equations with variable on both sides solution of linear equations in one variable

Seven times a two digit number is equal to four times the number obtained by reversing the order of digits. Find the number, if the difference between its digits is $3$. 

  1. $14$
  2. $25$
  3. $36$
  4. $47$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Let one's digit be $x$ and the tens be $x-3$


Number = $10(x-3) +x$ 

Reversed no. = $10x +x-3$ 

$ 7(10(x-3) +x) = 4(x-3 +10x)\ 70x -210 + 7x = 4x -12 +40x\ 33x = 198\ x = 6$ 

Number = $36$

Multiple choice maths equations and simple functions further equations solving linear equations with variable on both sides solution of linear equations in one variable

The sum of a $2$ digit number and the number obtained by reversing its digits is $154$. If the digits differ by $4$, find the number.

  1. $95$
  2. $73$
  3. $84$
  4. $62$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation
Let two digit number $=ab=10a+b$
Sum of number and reversed number $=154$
$(10a+b)+(10b+a)=154$
$a+b=14$
difference between digits$=\left|a-b\right|=4$
$a-b=\pm 4$
$(a+b=14)+(a-b=4)=2a=18$    $a=9,b=5$
$(a+b=14)-(a-b-4)=2a=10$      $a=5,b=9$
$\therefore   \text {Number}=95 (or)59$
Multiple choice maths equations and simple functions further equations solving linear equations with variable on both sides solution of linear equations in one variable

A number consists of two digits whose sum is 9. If 27 is added to the number, its digits are interchanged. Which of the given steps is CORRECT to find the number?
Step 1 : Let the units digit be x
Step 2 : Then, ten's digit = (9 - x)
$\therefore$  Number = 10 x (9 - x) + x
$\Rightarrow$  90 - 10x + x = (90 - 9x)
Step 3 : Adding 27 to the number 90 - 9x, we get 117 - 9x
Step 4 : Number with digits interchanged is 10x + (9 - x) = 9x + 9
Step 5 : 117 - 9x = 9x + 9
Step 6 : Therefore unit's digit = 6 and ten's digit = 3
Step 7 : Hence the number = 36.

  1. Only Step 4

  2. Both Step 1 and Step 2

  3. Step 1, 2, 3 and 4

  4. All steps are correct
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

In given question we have to find the number.

$\Rightarrow$  To find the numbers $7$ steps are given.
$\Rightarrow$  All $7$ steps are correct to find the required  number.
$\therefore$   Correct answer is option $D.$

Multiple choice maths knowing our numbers indian system of numeration numbers to 1 million numbers in indian and international systems

The least two digit composite number is

  1. $11$
  2. $12$
  3. $10$
  4. $16$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation
We know that-If a number has more than $2$ factors then it is a composite number.
$11$ is a prime number $\because$ it has only $2$ factors
$12$ is a composite number $\because$ it has more than $2$ factors
$10$ is a composite number $\because$ it has more than $2$ factors
$16$ is a composite number $\because$ it has more than $2$ factors
$\therefore\,10,12,16$ are composite numbers.
The least composite number is $10$
Multiple choice maths 5-digit numbers expanded form introduction to numbers and number systems numbers in general form

Numeral for sixty million and sixty six is

  1. $60,000,060$
  2. $60,000,066$
  3. $6,000,066$

  4. None of these
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

In international numbering system
The 1st period consists of - ones, tens and hundred.
The 2nd period consists of - thousand, $10$ thousand and $100 $ thousands.
The 3rd period consists of - million, $10$ million and $100$ million.
$\therefore $  Numeral for sixty million and sixty six $=60,000,066$
Option B is correct.

Multiple choice maths 5-digit numbers expanded form introduction to numbers and number systems numbers in general form

If a new number is formed by interchanging the tens and thousands place digits of $8727$, then what is the relation between them?

  1. New number is greater than original number.

  2. New number is smaller than original number.

  3. New number is equal to the original number.

  4. Can't be determined
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Original number $= 8727$
After interchanging tens and thousands of place digits, we get $2787$.
So, new member is smaller than original number.

Multiple choice maths 5-digit numbers expanded form introduction to numbers and number systems numbers in general form

In a two digit number, if number in units place is $8$ and number in tens place is $y$ then that number is __________.

  1. $y+8$
  2. $y+80$
  3. $10y+8$
  4. $80y$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Lets take an example of $23$
The digit at units place$=3$
The digit at tens place$=2$
The number$=2\times10+3=23$
In the question
The digit at units place is $8$
Thus, the number $=y\times10+8=10y+8$

Multiple choice maths 5-digit numbers expanded form introduction to numbers and number systems numbers in general form

Numeral for ninety million ninety thousand ninety is

  1. $9090095$
  2. $90090090$
  3. $909090$

  4. None of these
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation
We know that,

$1$ million $= 1000000$, therefore, $90$ million $= 90000000$

$1$ thousand $= 1000$, therefore, $90$ thousand $= 90000$

Thus, ninety million ninety thousand ninety is

$=90000000+90000+90=90090090$

Hence, numeral for ninety million ninety thousand ninety is $90090090$.