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Number sense : A persons ability to use and understand numbers:-

v Knowing their relative valuesv Use them to make judgementsv Usetheminflexiblewayswhenadding,subtracting,

multiplying or dividingv Developusefulstrategieswhencountingmeasuring

or estimating

Zero

Zeroisthefirstnumberinthecountinganditiswrittenas 0. The number zero represents having no value. This canbeunderstandbyfollowingexample:

1.Suppose there are 5 birds sitting on the branch of thetree.

2.Outof5birds,2flyaway,sonow 3 birds are sitting on the branchofthetree.

3.The remaining birds also flyaway and now there are zero birdsonthebranch.

Numbers from 0 to 9 are called one digit numbers.Numbersfrom10to99arecalledtwodigitnumbers.

Historical Preview

vZero is the only number which cannot berepresented in Roman.

vZero was discovered byan Indian mathematiciannamed Aryabhatta.

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Concept Notes: Number Sense

Class-1: Mathematics

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Number l i Ne

Arrangmentofnumbersfromlefttorightinalineinincreasingorderiscallednumberline.Forexamplenumbersfrom0to10areshowninthenumberlineasfollowing.

01 2 3 4 5 6 7 8 9 10

Number line is useful in addition and subtraction and also tells the relation between thenumbers.Wewilllearnaboutnumberlineinhigherclasses.

p lace va lue of a Number

In any two digit number first numberfromrightiscalledonesandsecondnumberfromrightiscalledtens.Forexample:

eg. first number from right

Tens Ones

3 5

second number from right

→ 35 has 5 ones and 3 tens

bu i ld iNg Numbers

Building numbers from 11 to 20: Addition method is used for building of numbers for example.Whenweadd1to10thenitwillform11.Similarly,2isaddedin10togetnumber12.

Tens Ones1 1

Tens Ones1 2

Tens Ones2 0

Tens Ones1 9

Eleven

Twelve

Nineteen

Twenty

11

19

20

10 1

2

12

10

910

10 10Building Numbers From 21 to 50:Now,letustakesomeexamplestobuildnumbersfrom21to 50.When we add 1 to 20 then it will form 21.LetusunderstandwithanexampleHere = 10

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10 10 1

10 10 10

10 10 5

10 10 10 9

10 10 10 10 8

10 10 10 10 10

Twenty one

Twenty five

Thirty

Thirty Nine

Fourty Eight

Fifty

211

Tens Ones

25

30

39

48

50

5

0

9

8

0

2

2

3

3

4

5

before , a f t er aNd be tweeN

Onemorethananumbercomesafterit.Onelessthananumbercomesbeforeit.Forexample:

17 is before 18 18 is between 17 & 19

19 is after 18

compar iNg Numbers

Howwillyoucomparetwonumbers?Greaterthan(>),lessthan(<)orequalto(=)signsareusedtocomparenumbers.For example:

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Here 3 is less than 7.

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8 is more than 6.

order iNg Numbers

Numbers, when arranged from the smallest to the largest are said to be inascending or increasing order.Forexample:

Numbers canbearrangedinascendingorincreasingnumberasfollowing.

from the lowest step to the highest step

9

15

25

Numbers when arranged from the largest to the smallest are said to be in descending or decreasing order.Example:

from the highest step to the lowest step

9

15

25

backward couN t iNg

Inbackwardcountingthenumbersarewritteninreverseorder.For example

1. 50 49 48 47 46 45 44 43 42 4140 39 38 37 36 35 34 33 32 3130 29 28

2. 10 9 8 7 6 5 4 3 2 1

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s k i p couN t iNg

Inskipcounting,valueofthenumbersincreaseuniformlyForexample:(a) Skipcountingof2canbewrittenas— 2, 4, 6, 8, 10...(b) Skipcountingof3canbewrittenas— 3, 6, 9, 12, 15...