Question

A teacher has 21 red pens. If the ratio of red pens to blue pens is 3:1 how many pens did she have total?

Answer 1

Answer on Question #46058 – Math - Algebra

A teacher has 21 red pens. If the ratio of red pens to blue pens is 3:1 how many pens did she have total?

Solution

Let’s mark blue pens as $x$, then, in total:

$$S = 21 + x$$

We know that

$$21: x = 3: 1 \rightarrow x = \frac{21}{3} = 7$$

Now we know how many blue pens teacher has. Thus, in total she has:

$$S = 21 + 7 = 28$$

Answer: teacher has 28 pens

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