Henry is buying school supplies for the start of the school year. For every 3 pencils he buys 2 pens. If Henry buys 21 pencils, how many total pencils and pens did Henry purchase?

Remark

The total number of items bought is represented by 2 + 3 = 5. So for pencils to pencils + pens his ratio of pencils to total is 3/5

Equation

3/5 = 21 / x Cross multiply

3x = 5 * 21

3x = 105

x = 105/3

x = 35

Conclusion

The total number of pens and pencils that he bought was 35 <<< Answer.

Note

He bought 35 - 21 = 14 pens. That should be 2/5 of the total.

Check

2/5 * 35 = 70/5 = 14 So it checks.