The "equal" sign: Are you using it correctly?
THE equal sign is a mathematical symbol used to indicate equality. Apparently invented in the mid-16th century by Welsh mathematician Robert Recorde, the equal (or equals) sign is placed between the things stated to be equal.
So it can say or suggest the following:
- two different symbols (or expressions) have the same value.
- two different calculations or expressions have the same value.
- the value of a number or quantity is the same as the value of another expression.
Notice the emphasis on "same value". This refers to precision in representation.
Precision is key in mathematics
A person who does not write exactly what he or she means does not know how to read precisely what is written in their notes and textbooks, and so can be easily confused when revisiting their notes.
This is of particular importance in mathematics. Confusion about notation, what is proper or not, leads to errors in calculations and in problem solving.
Parent facilitators and other stakeholders in the child's education can help by marking what is actually written, not what the child might have meant. This will encourage the child to learn to write precisely, starting from primary school-going age.
Marks deduction for improper use
Be aware that in problem sum solutions that carry four or five marks and for those working steps where marks are allocated for method, marks may be deducted for the wrong use of the sign. See the examples below which display both correct and incorrect usage of the equal sign.
Question: 170 ml - 120 ml
170 ml - 120 ml = 50 ml
170 - 120 = 50
170 - 120 -> 50
Ans: 50 ml
170 - 120 = 50 ml
Question: Express 70 as a percentage of 200.
70/200 x 100% = 35%
70/200 x 100 = 35%
Question: Find 10% of 5 kg.
10% of 5 kg -> 0.5 kg
10% of 5 kg -> 500 g
10% = 0.5 kg
10% = 500 g
Question: A pen with a retail price of $80 was sold at a discount of 20%. Find the discounted price.
100% -> 80
1% -> 80/100 -> 0.80
20% -> 0.80 x 20 -> 16
Discounted price -> 80 - 16
100% = 80
1% = 80/100 = 0.80
20% = 0.80 x 20 = 16