Question

To a box that contained 50 pencils 10 out of which were red several more red pencils were added. Now 50% of all pencils in this box are red. How many red pencils were added to the box?

Answer 1

The total number of pens initially there are :

50 pens

Let the number of red pens added be x.

We now have :

(x + 10) red pens

The new total is :

50 + x

The percentage of red is :

(x + 10) / (50 + x) × 100 = 0.5

(100x + 1000) / (50 + x) = 50

100x + 1000 = 50(50 + x)

100x + 1000 = 2500 + 50x

100x - 50x = 2500 - 1000

50x = 1500

X = 1500/50

X = 30

30 red pencils were added.