Question

Find the value of $39-35+7-\left( -4 \right)+21$.

Answer 1

Hint: For solving this question, we need to understand a basic rule called BODMAS. According to that, brackets are solved first, then exponents (order), then division, then multiplication, then addition, and at last subtraction. Here we will apply this rule and solve it. One more property of integers will be used which states that multiplication of two negative signs cancels out to become positive sign i.e. $\left( - \right)\left( - \right)=\left( + \right)$.

Complete step-by-step solution
Here we are given the expression as $39-35+7-\left( -4 \right)+21$.
We will use BODMAS here. B stands for bracket which means brackets will be solved first. O stands for the order which means the order of any number is solved next. D stands for division and division is solved next. M is for multiplication, A is for addition and S is for subtraction.
In this expression, we can see that we have a bracket here, so it will be solved first.
Now according to property of integers, multiplication of two negative signs cancels out to become positive sign i.e. $\left( - \right)\left( - \right)=\left( + \right)$. Hence, here (-)(-4) will become +4. So our expression becomes $39-35+7+4+21$.
Now since we are left with addition and subtraction only and addition is given priority. So let us solve 7+4 first. $7+4=11$. So our expression becomes $39-35+11+21$.
Solving 11+21 we get $11+21=32$ so our expression becomes $39-35+32$.
Now 39 and 32 have positive signs, so rearranging we get $39+32-35$.
Solving addition first $39+32=71$ so our expression reduces to 71-35.
Now solving the last subtraction we get $71-35=36$.
Hence 36 is our final answer.

Note: Students should take care of signs while solving these sums. Students should note that the sign preceding (positive or negative) is considered as the sign of the number. For example, in the given expression 35 has a negative sign whereas 21 has a positive sign.