# CBSE Class 10-Mathematics: Chapter –4 Quadratic Equations Part 25

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**Question 11:**

A factory kept increasing its output by the same percent ago every year. Find the percentage if it is known that the output is doubled in the last two years.

**Answer:**

According to question,

**Question 12:**

Two pipes running together can fill a cistern in minutes. if one pipe takes minutes more than the other to fill it, find the time in which each pipe would fill the cistern.

**Answer:**

Let the faster pipe takes minutes to fill the cistern and the slower pipe will take minutes.

According to question,

**Question 13:**

If the roots of the equation are equal, prove that

**Answer:**

For equal root s,

**Question 14:**

Two circles touch internally. The sum of their areas is and the distance between their centers is . Find the radii of the circles.

**Answer:**

Let be the radius of two circles

According to question,

Put the value of in eq. …(i)

When