Question

If the sum of three consecutive natural numbers starting from $x$ is $21$, find all three numbers using a simplified algebraic expression for the sum.

• A. $6,7$ and $8$
• B. $5,6$ and $7$
• C. $7,8$ and $9$
• D. $3,4$ and $5$

Answer 1

The correct option is A $6,7$ and $8$

Given:
Smallest of the three numbers $=x$
So, the three consecutive natural numbers would be $=x,x+1$, and $x+2$

The sum of these $3$ natural numbers is given as $21$, i.e.,
$x+(x+1)+(x+2)=21$
Combining the like terms together using commutative property of addition,
$3x+3=21$
$\Rightarrow 3x=18$
$\Rightarrow 3x÷3=18÷3$
$\Rightarrow x=\frac{18}{3}=6$
Hence, the consecutive numbers are $6,7,$ and $8.$