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 numbers and place value face value of digit large numbers general form of number

The digit in the units place of the number $2015!+3^{7886}$ is

  1. $1$
  2. $3$
  3. $7$
  4. $9$
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

$2015! + 3^{7886}$

$2015! \Rightarrow$ Unit digit $\Rightarrow \underline { 0 }$

$3^{7886}=3^{4n+2}$, So unit digit $\Rightarrow 9$

$\therefore 0+9 \Rightarrow \underline{9}$.

$\therefore$ Digit at unit place $\Rightarrow 9$ 

Multiple choice maths numbers and place value face value of digit large numbers general form of number

How many times does the digit $1$ appear in numbers from $1$ to $100$?

  1. $18$
  2. $19$
  3. $20$
  4. $21$
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

$\Rightarrow$  1–10 = 2 times

$\Rightarrow$  11–20 = 10 times
$\Rightarrow$  21–30 = 1 time
$\Rightarrow$  31–40 = 1 time
$\Rightarrow$  41–50 = 1 time
$\Rightarrow$  51–60 = 1 time
$\Rightarrow$  61–70 = 1 time
$\Rightarrow$  71–80 = 1 time
$\Rightarrow$  81–90 = 1 time
$\Rightarrow$  91–100 = 2 times
$\Rightarrow$  $Total = 2+10+1+1+1+1+1+1+1+2=21$
$\therefore$   The digit 1 appear in number from 1 to 100 is $21$.

Multiple choice maths numbers and place value face value of digit large numbers general form of number

A number consists of two digits whose sum is $11$. If $27$ is added to the number, then the digits change their places. What is the number?

  1. $47$
  2. $65$
  3. $83$
  4. $92$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Let the ten's digit be $x$. Then, unit's digit $= \left(11 - x\right)$.
So, number $= 10x + \left(11 - x\right) = 9x + 11$.
Therefore $\left(9x + 11\right) + 27 = 10 \left(11 - x\right) + x  \Leftrightarrow  9x + 38 = 110 - 9x \Leftrightarrow   18x = 72 \Leftrightarrow   x = 4$.
Thus, ten's digit $= 4$ and unit's digit $= 7$.
Hence, required number $= 47$.

Multiple choice maths decimal fractions rounding decimals non-terminating recurring decimals in rational numbers rounding off decimals rounding of decimals

A $3$ digit id a $3$ digit number (not starting with zero) which reads the same backwards as forwards. For example $171$. The sum of all even $3$ digit palindromes, is 

  1. $22380$
  2. $25700$
  3. $22000$
  4. $22400$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

A 3-digit palindrome is of the form ABA. For it to be even, A must be 2, 4, 6, or 8. B can be 0-9. For each A, there are 10 possibilities for B. Summing these values: 202+212+...+292, 404+414+...+494, etc. The sum is 22380.

Multiple choice maths number work indian place value chart place value of digit largest and smallest numbers

If number read " Ten thousand eight hundred six." Find missing digit.
$1\ \ _,806$

  1. $1$
  2. $10$
  3. $2$
  4. $0$
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Number reads Ten thousand eight hundred six.

$1$ is at ten thousand's place, $0$ at thousand's place, $8$ at hundred's place, $0$ at ten's place and $6$ at one's place.

This written in numeral is $10,806$

Missing digit is $0$ in thousands place