Question

How do u evaluate \[21 - 2 \times 2 \div 4\] ?

Answer 1

Hint: The four basic arithmetic operations in Maths are: Addition, Subtraction, Multiplication and Division. The algebraic expression should be any one of the forms and hence to evaluate the given expression, we must know PEMDAS rule, as per PEMDAS rule, we have to calculate the expressions given in the parentheses first, hence, second preference in this rule is given to the exponents \[{x^n}\] , next we perform the arithmetic operations \[\left( { \div or \times , + , - } \right)\] i.e., division, multiplication, addition and then subtraction and then simplify it.

Complete step-by-step answer:
Given,
 \[21 - 2 \times 2 \div 4\]
According to PEMDAS rule, we need to perform multiplication or division from left to right, whichever comes first in the equation. Hence, according to PEMDAS rule we need to perform multiplication to the terms for \[2 \times 2\] , hence we get:
 \[ \Rightarrow 21 - 4 \div 4\]
Next, we need to perform division for \[4 \div 4\] , we have:
 \[ \Rightarrow 21 - 1\]
Simplify the terms, we get:
 \[ \Rightarrow 20\]
Therefore,
 \[21 - 2 \times 2 \div 4 = 20\]
So, the correct answer is “20”.

Note: The key point to evaluate the given expression is that we must know to perform addition, subtraction, multiplication and division. And we must know PEMDAS rule to simplify the expression. The full form of PEMDAS rule i.e.,
P – Parentheses
E – Exponents
MD- Multiplication and Division
AS – Addition and Subtraction.