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Having fun with pocket calculators and negative numbers

Educator section


5. a) 108

b) 9

c) 13

d) 68

e) 14

f) 4

g) 48

h 72

i) 200

j) 18 000

k) 20

l) 9

m) R238

n) R6 080

o) 54

Leaner section


Activity: fun with the pocket calculator [lo 1.9.2

Fun with the pocket calculator

1. Did you know that pocket calculators are also able to “speak”? Take you pocket calculator and key in the following: 0,65 + 0,1234 =

Now turn your calculator upside-down. What do you read?


In this module we will be learning how to use the pocket calculator effectively in order to make calculating easy.


5 000 years ago the Babylonians designed a counting frame that they called an abacus. The Chinese still use a variation of this counting machine. Their abacus consists of beads that are moved along the rods of a counting frame.

In 1642 Blaise Pascal, who lived in France, designed a counting machine that was operated by turning knobs, but it was too expensive to produce.

Charles Babbage, a British mathematician, began working on a steam-driven analytical engine in 1830. For 37 years he worked on this engine that was able to do a variety of calculations, but died before he could finalise the design.


Work with a friend and find the following keys on your pocket calculator:

AC = Deletes everything, including the memory
C = Clears the screen
CE / CM = Clears the memory
Min / M / M+ _____________________________________
STO = Stores in the memory / adds
M- = Subtracts from the memory
RCL / x M _____________________________________
MR / RM = Recalls the memory
O m / O m = You did not clear the memory

Does your pocket calculator have another key that must be pressed to do the above? Write it here:






We have pocket calculators and scientific calculators.The latter are used for more complicated calculations.Compare your pocket calculator with those of your classmatesto see how they agree or differ.

5. Before we continue working with the pocket calculator, we are going to use some brainpower! Complete the following mental calculation test as quickly and accurately as possible:

a) 12 × 9 = __________

b) __________ × 7 = 63

c) 48 + __________ = 61

d) __________ - 18 = 50

e) 63 - __________ = 49

f) (12 × 8) + __________ = 100

g) 8 × 3 × 3 = __________

h) __________ ÷ 8 = 9

i) 80 × 40 = __________

j) 300 × 60 __________

k) 500 ÷ 25 = __________

l) one third of 27 = __________

m) R2,38 × 100 = __________

n) R6,08 × 1 000 = __________

o) __________ ÷ 6 = 9


Complete by colouring in the appropriate block:

This was GOOD AVERAGE POOR work!


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 1.9: We know this when the learner uses a range of techniques to perform calculations including:

1.9.2: using a calculator.

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Source:  OpenStax, Mathematics grade 7. OpenStax CNX. Sep 16, 2009 Download for free at http://cnx.org/content/col11075/1.1
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