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Mathematics

Number concept, addition and subtraction

Addition

Educator section

Memorandum

1. Look at the unit’s digit.

If it is 5 or more, the tens digit becomes one more.

If it is 4 or less, the tens digit remains the same.

2. Look at the tens digit.

If it is 5 or more, the hundreds digit becomes one more.

If it is 4 or less, the hundreds digit remains unchanged.

3. Look at the hundreds digit.

If it is 5 or more, the thousands digit becomes one more.

If it is 4 or less, the thousands digit remains the same.

2.

2.1 20 + 10 + 20 = 50

2.2 30 + 10 + 50 = 90

2.3 10 + 20 + 20 = 50

2.4 100 + 200 + 300 = 600

2.5 200 + 100 + 100 = 400

3. “Estimated answer” and “Difference” will be different as a result of the method

applied. Pocket calculator gives correct answer.

4.

a) 279

b) 1 660

c) 6 581

d) 2 843

5. Answers will vary – many combinations possible

6. 35 + 15; 47 + 3; 23 + 27

50 + 150; 25 + 175; 10 + 190; 180 + 20; 170 + 30

250 + 750; 400 + 600; 900 + 100; 200 + 800; 990 + 10

6. 250 + 750; 125 + 825; 950 + 50; 450 + 550; 225 + 775; 415 + 585

7. 5 000 + 400 + 80 + + 9 + 300 + 60 + 2 + 1 000 + 500 + 70

= (5 000 + 1 000) + (400 + 300 + 500) + (80 + 60 + 70 +) + (9 + 2)

= 6 000 + 1 200 + 210 + 11

= 7 421

Leaner section

Content

Activity: to estimate and calculate by selecting and using suitable operations [lo 1.8]

  • Now practise your skill at estimating with confidence the answers by rounding off numbers.

1. It is important that we consider once again what rounding off is, and how it is done. Explain to a friend how we round off to the nearest 10, 100 and 1 000.

2. Now work in groups of three and see who is able to calculate the answers without a pocket calculator by rounding off to the closest 10 or 100. (You may not write anything down!)

2.1 16 + 11 + 19

2.2 34 + 9 + 52

2.3 2 + 15 + 23

2.4 141 + 208 + 339

2.5 182 + 149 + 106

3. Look carefully at the following example:

32 + 87 + 96 + 42 becomes

30 + 90 + 100 + 40 (rounded off to the closest 10)

Therefore the answer is approximately 260.

  • When we want to add larger numbers, we can round off to the closest 100:

138 + 759 + 304 becomes

100 + 800 + 300

Therefore the answer will be roughly 1 200.

DID YOU KNOW?

  • We can also round numbers off to a lower or upper limit!

e.g. 62 + 75 + 94 + 45

Lower limit: 60 + 70 + 90 + 40 = 260

Upper limit: 70 + 80 + 100 + 50 = 300

The correct answer will therefore be between

260 and 300.

4. Now complete the table by rounding off the numbers according to the method that you prefer. Estimate the answer first. Then calculate the correct answer with a pocket calculator. Finally write down the difference between the two answers.

Calculation Estimated answer Calculator Difference
E.g. 308 + 475 300 + 480 = 780 783 3
a) 67 + 98 + 114
b) 896 + 723 + 41
c) 1 892 + 4 689
d) 2 458 + 294 + 91

TIME FOR SELF-ASSESSMENT!

Colour the correct box:

I am able to add by rounding off to the closest 10, 100 or 1 000 mastered ** have not mastered yet

** Ask your educator to give you some more examples that you can do at home!!

5. There are also other techniques or computations (other than rounding off) that you can use to calculate answers quickly. Look carefully at the examples and try to add more number combinations.

6. Look at the numbers in the diagram below. By finding as many as possible addition strings that give a sum of 1 000, you can calculate the sum of all the numbers in a jiffy! How many do you see? Colour them in the same colour.

250
585
125
750 825 50
950
450
550 775 415 225 316 775 415

DO YOU STILL REMEMBER?

We can use grouping to add up. Look carefully at the example!

  • = 370 + 245 + 684

= 300 + 70 + 200 + 40 + 5 + 600 + 80 + 4

= (300 + 200 + 600) + (70 + 40 + 80) + (5 + 4)

= 1 100 + 190 + 9

  • = 1 299

7. Use this method to calculate:

5 489 + 362 + 1 570

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Assessment

Learning Outcome 1: The learner will be able to recognise, describe and represent numbers and their relationships, and to count, estimate, calculate and check with competence and confidence in solving problems.

Assessment Standard 1.8: We know this when the learner estimates and calculates by selecting and using operations appropriate to solving problems.

Questions & Answers

find the 15th term of the geometric sequince whose first is 18 and last term of 387
Jerwin Reply
I know this work
salma
The given of f(x=x-2. then what is the value of this f(3) 5f(x+1)
virgelyn Reply
hmm well what is the answer
Abhi
how do they get the third part x = (32)5/4
kinnecy Reply
can someone help me with some logarithmic and exponential equations.
Jeffrey Reply
sure. what is your question?
ninjadapaul
20/(×-6^2)
Salomon
okay, so you have 6 raised to the power of 2. what is that part of your answer
ninjadapaul
I don't understand what the A with approx sign and the boxed x mean
ninjadapaul
it think it's written 20/(X-6)^2 so it's 20 divided by X-6 squared
Salomon
I'm not sure why it wrote it the other way
Salomon
I got X =-6
Salomon
ok. so take the square root of both sides, now you have plus or minus the square root of 20= x-6
ninjadapaul
oops. ignore that.
ninjadapaul
so you not have an equal sign anywhere in the original equation?
ninjadapaul
hmm
Abhi
is it a question of log
Abhi
🤔.
Abhi
I rally confuse this number And equations too I need exactly help
salma
But this is not salma it's Faiza live in lousvile Ky I garbage this so I am going collage with JCTC that the of the collage thank you my friends
salma
Commplementary angles
Idrissa Reply
hello
Sherica
im all ears I need to learn
Sherica
right! what he said ⤴⤴⤴
Tamia
hii
Uday
hi
salma
what is a good calculator for all algebra; would a Casio fx 260 work with all algebra equations? please name the cheapest, thanks.
Kevin Reply
a perfect square v²+2v+_
Dearan Reply
kkk nice
Abdirahman Reply
algebra 2 Inequalities:If equation 2 = 0 it is an open set?
Kim Reply
or infinite solutions?
Kim
The answer is neither. The function, 2 = 0 cannot exist. Hence, the function is undefined.
Al
y=10×
Embra Reply
if |A| not equal to 0 and order of A is n prove that adj (adj A = |A|
Nancy Reply
rolling four fair dice and getting an even number an all four dice
ramon Reply
Kristine 2*2*2=8
Bridget Reply
Differences Between Laspeyres and Paasche Indices
Emedobi Reply
No. 7x -4y is simplified from 4x + (3y + 3x) -7y
Mary Reply
how do you translate this in Algebraic Expressions
linda Reply
Need to simplify the expresin. 3/7 (x+y)-1/7 (x-1)=
Crystal Reply
. After 3 months on a diet, Lisa had lost 12% of her original weight. She lost 21 pounds. What was Lisa's original weight?
Chris Reply
what's the easiest and fastest way to the synthesize AgNP?
Damian Reply
China
Cied
types of nano material
abeetha Reply
I start with an easy one. carbon nanotubes woven into a long filament like a string
Porter
many many of nanotubes
Porter
what is the k.e before it land
Yasmin
what is the function of carbon nanotubes?
Cesar
I'm interested in nanotube
Uday
what is nanomaterials​ and their applications of sensors.
Ramkumar Reply
what is nano technology
Sravani Reply
what is system testing?
AMJAD
preparation of nanomaterial
Victor Reply
Yes, Nanotechnology has a very fast field of applications and their is always something new to do with it...
Himanshu Reply
good afternoon madam
AMJAD
what is system testing
AMJAD
what is the application of nanotechnology?
Stotaw
In this morden time nanotechnology used in many field . 1-Electronics-manufacturad IC ,RAM,MRAM,solar panel etc 2-Helth and Medical-Nanomedicine,Drug Dilivery for cancer treatment etc 3- Atomobile -MEMS, Coating on car etc. and may other field for details you can check at Google
Azam
anybody can imagine what will be happen after 100 years from now in nano tech world
Prasenjit
after 100 year this will be not nanotechnology maybe this technology name will be change . maybe aftet 100 year . we work on electron lable practically about its properties and behaviour by the different instruments
Azam
name doesn't matter , whatever it will be change... I'm taking about effect on circumstances of the microscopic world
Prasenjit
how hard could it be to apply nanotechnology against viral infections such HIV or Ebola?
Damian
silver nanoparticles could handle the job?
Damian
not now but maybe in future only AgNP maybe any other nanomaterials
Azam
Hello
Uday
I'm interested in Nanotube
Uday
this technology will not going on for the long time , so I'm thinking about femtotechnology 10^-15
Prasenjit
can nanotechnology change the direction of the face of the world
Prasenjit Reply
At high concentrations (>0.01 M), the relation between absorptivity coefficient and absorbance is no longer linear. This is due to the electrostatic interactions between the quantum dots in close proximity. If the concentration of the solution is high, another effect that is seen is the scattering of light from the large number of quantum dots. This assumption only works at low concentrations of the analyte. Presence of stray light.
Ali Reply
the Beer law works very well for dilute solutions but fails for very high concentrations. why?
bamidele Reply
how did you get the value of 2000N.What calculations are needed to arrive at it
Smarajit Reply
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Source:  OpenStax, Mathematics grade 5. OpenStax CNX. Sep 23, 2009 Download for free at http://cnx.org/content/col10994/1.3
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