Robin is 6 years old.
What is equation?
"It is a mathematical statement which consists of equal symbol between two algebraic expressions."
For given question,
Let 'a' be the current age of Robin and 'b' be the age of his grandmother.
Robin's grandmother is 7 times older than him.
We write this in equation form,
⇒ b = 7 × a .........................(i)
After 12 years, the age of Robin = 12 + a and the age of his grandmother would be 12 + b.
In 12 years, she will be 3 times as old as him.
We write this in equation form,
⇒ (12 + b) = 3 × (12 + a)
⇒ 12 + b = 36 + 3a
⇒ 3a - b = -24 ....................(ii)
Substitute b = 7a in above equation.
⇒ 3a - (7a) = -24
⇒ -4a = -24
⇒ a = 6 years
Substitute this value of a in equation (i),
⇒ b = 6 × 7
⇒ b = 42 years
Therefore, Robin is 6 years old.
Learn more about an equation here:
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