When amy's cd's are fully charged, it lasts for 9 hours. she only charged it 9/12 full, how long will it last?

6.75 hours.

Step-by-step explanation:

Given:

Time lasted on full charge = 9 hours.

CD's charged by Amy = of full charge.

Using unitary method, we solve for the time the CD's will last for given charge.

This can be done by multiplying the time for 1 complete charge and the fraction of the charge done.

∵ Time required for 1 complete charge = 9 hours.

∴ Time required for of full charge =

⇒ Time required for of full charge =

Therefore, the time it will last for of full charge is 6.75 hours.

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step-by-step explanation: