✏️ Question:

• Echo is twice as old as his sister Nikki. The sum of their ages is 21. How old are they?

✏️ Answer:

• 2n + 21 or 3n = 21

✏️ Step-by-step explanation:

• The word twice implies multiplication, sum means addition and the phrase "is" with be replaced with the symbol "=".
• Let n be the unknown age of Echo (Echo=n) and twice means double the age of Nikki (Nikki = 2n).

➡️ So, we express this as 2n + 21 or 3n = 21

➡️ 3n = 21 gives you a complete information because of the relation symbol ( = ) and 21 as the result. Thus, we call this is an algebraic equation.

➡️ While 4n + 6 does not give a complete information for it has no answer and no relation symbol and we call this an algebraic expression.

Answer:

Echo= 14, Nikki= 7

Step-by-step explanation:

2x + x = 21

3x= 21

x= 7