2
$\begingroup$

I am new to writing equations and have to write and solve the following:

Kevin is $7$ less than three times Maria's age. If Kevin is $17$, how old is Maria?

I think Maria is $30$ if Kevin is $17$ because Kevin is $7$ less than $3$ times Maria's age but I don't know how to put it in the correct equation format. Do I need more than one variable? This is where my confusion is.

Thanks for any help or tips!

Edited to add - I think Maria is $30$ because if Kevin is $17$ and he is $7$ less than three times Maria's age $(17-7=10)$ and $10\times 3 =30$.

  • 0
    Firstly, you should be providing at least written reasoning for your answer, a simple calculation shows that you have made a mistake – 2017-01-18
  • 0
    Kevin's age is known, so you only need one variable for Maria's age. – 2017-01-18
  • 0
    Thanks for the suggestion - I added it to my original question. – 2017-01-18
  • 0
    "I think Maria is $30$ if Kevin is $17$ because Kevin is $7$ less than $3$ times Maria's age" No. If Kevin is 17 then Maria would be 8. – 2017-01-18

3 Answers 3

1

You only need one variable.

Let Maria's age be $x$. So $3x-7=17$ since Kevin is $17$. Solving, we get $x=8$. So Maria is $8$ years old.

In other words, $3x-7=17$ is the equation you want.

(If you try to have Maria being $30$, then Kevin's age would be $3\times30-7=83$!! Which I don't think is $17$. Wait, am I wrong?)

  • 1
    Thank you! I was totally off in my reasoning (and poor Maria - I aged her!) – 2017-01-18
1

"Kevin" is "$7$ less than" " three times of Maria's age".

Let $K$ be kevin's age and $M$ be Maria's age. I can translate the statement above into

$K$ is "$7$ less than " $3M$".

$K$ is a smaller number here and the difference is $7$.

$$K=3M-7$$

Now, we can use the knowledge that $K=17$ in the equation above and solve for $M$.

$$17=3M-7$$

  • 0
    Thank you! Clearly my way of thinking of this problem was way off! – 2017-01-18
-1

Kevin is $17$, so add $7$ to $17$, then divide by $3$.