# Past Papers’ Solutions | Cambridge International Examinations (CIE) | AS & A level | Mathematics 9709 | Pure Mathematics 1 (P1-9709/01) | Year 2011 | May-Jun | (P1-9709/11) | Q#2

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**Question**

The volume of a spherical balloon is increasing at a constant rate of 50 cm3 per second. Find the rate of increase of the radius when the radius is 10 cm. [Volume of a sphere ]

**Solution**

** i.
**

We are given that;

We are required to find rate of change of radius;

Therefore;

For rate of change of radius;

We have so we need to find .

Expression for the volume of the sphere is;

Therefore;

Rate of change of with respect to

Therefore, rate of change of volume of sphere is;

Rule for differentiation of

Rate of change

Hence rate of change of volume when

Finally;

## Comments

## yes

thanks