HOW TO FIND THE UNIT DIGIT IN THE PRODUCT

To identify the unit digit of a number with some power, we must be aware of cyclicity.

Cyclicity of Numbers

Cyclicity of any number is about the last digit and how they appear in a certain defined manner.

Example 1 :

Let us consider the values of 2n, where n = 1, 2, 3, ...........

2 =  2

22  =  4

23  =  8

24  =  16

25  =  32

26  =  64

In the above calculations of 2n

We get unit digit 2 in the result of 2n, when  n  =  1.

Again we get 2 in the unit digit of 2n, when n  =  5.

That is, in the fifth term.

So, the cyclicity of 2 is 4.

Example 2 :

Let us consider the values of 3n, where n = 1, 2, 3, ...........

31  =  3

32  =  9

33  =  27

34  =  81

35  =  243

36  =  729

In the above calculations of 3n

We get unit digit 3 in the result of 3n, when  n  =  1.

Again we get 3 in the unit digit of 3n, when n  =  5.

That is, in the fifth term.

So, the cyclicity of 3 is 4.

In the same way, we can get cyclicity of others numbers as shown below.

Cyclicity of 4 and 5

 Cyclicity of 441  =  442  =  1643  =  6444  =  256The cyclicity of 4 is 2. Cyclicity of 551  =  552  =  2553  =  125The cyclicity of 5 is 1.

Cyclicity of 6 and 7

 Cyclicity of 661  =  662  =  3663  =  216The cyclicity of 6 is 1. Cyclicity of 771  =  772  =  4973  =  34374  =  240175  =  16807The cyclicity of 7 is 4.

Cyclicity of 8, 9 and 10

 Cyclicity of 881  =  882  =  6483  =  51284  =  409685  =  32768Cyclicity of 8 is 4. Cyclicity of 991  =  992  =  8193  =  729Cyclicity of 9 is 2.Cyclicity of 10101  =  10102  =  100Cyclicity of 10 is 1.

Cyclicity of Numbers - Summary

 Number12345678910 Cyclicity of a number1442114421

Solved Problems

Example 1 :

Find the unit digit in the product :

(3547)153 x (251)72

Solution :

In (3547)153, unit digit is 7.

The cyclicity of 7 is 4. Dividing 153 by 4, we get 1 as remainder.

71  =  7

So, the unit digit of 7153 is 7.

In 25172, unit digit is 1.

Because 1 has the cyclicity 1, the unit digit of 25172 is 1.

By multiplying the unit digits, we get

7 x 1  =  7

Therefore, the unit digit of the expression

(3547)153 x (251)72 is 7.

Example 2 :

Find unit digit in the product :

(6374)1793 x (625)317 x (341)491

Solution :

In (6374)1793, unit digit is 4.

The cyclicity of 4 is 2. Dividing 1793 by 4, we get 1 as remainder.

41  =  4

So, the unit digit of (6374)1793 is 4.

In (625)317, unit digit is 5.

Since 5 has the cyclicity 1, the unit digit of (625)317 is 5.

In (341)491, unit digit is 1.

Since 1 has the cyclicity 1, the unit digit of (341)491 is 1.

By multiplying the unit digits, we get

4 x 5 x 1  =  20

The unit digit of 20 is '0'.

Therefore, the unit digit of the expression

(6374)1793 x (625)317 x (341)491 is 0

Kindly mail your feedback to v4formath@gmail.com

Recent Articles

1. SAT Math Questions and Answers (No Calculator)

Dec 01, 23 08:59 PM

SAT Math Questions and Answers (No Calculator)

2. Linear Equations in One Variable

Dec 01, 23 11:01 AM

Linear Equations in One Variable