A lens has a focal length of, $-10 \mathrm{cm}$. What is the power of the lens and what is its nature?

A convex lens of power $5 \mathrm{D}$ and a concave lens of power $7.5 \mathrm{D}$ are placed in contact with each other. What is the:

Power of this combination of lenses? 

A convex lens of power $5 \mathrm{D}$ and a concave lens of power $7.5 \mathrm{D}$ are placed in contact with each other. What is the:

Focal length of this combination of lenses?

A convex lens of focal length $25 \mathrm{cm}$ and a concave lens of focal length $10 \mathrm{cm}$ are placed in close contact with one another.

What is the power of this combination?

A convex lens of focal length $25 \mathrm{cm}$ and a concave lens of focal length $10 \mathrm{cm}$ are placed in close contact with one another.

What is the focal length of this combination?

A convex lens of focal length $25 \mathrm{cm}$ and a concave lens of focal length $10 \mathrm{cm}$ are placed in close contact with one another.

Is this combination converging or diverging?