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# Amy had 30 CDs....

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Amy had 30 CDs

The mean playing time of these 30 CDs was 42 minutes.

Amy sold 5 of her CD.

The mean playing time of the 25 CDs left was 42.8 minutes.

Calculate the mean playing time of 5 CDs that Amy sold.

May 7, 2015

### Best Answer

#1
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Total time of all 30 can be written two ways:

25*42.8 + 5*m where m is mean time of the 5 CDs that were sold, and

30*42

So 25*42.8 + 5m = 30*42

See if you can find m from this.

.

May 7, 2015

### 3+0 Answers

#1
+8
Best Answer

Total time of all 30 can be written two ways:

25*42.8 + 5*m where m is mean time of the 5 CDs that were sold, and

30*42

So 25*42.8 + 5m = 30*42

See if you can find m from this.

.

Alan May 7, 2015
#2
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Thanks Alan, I always like these types of questions :)

May 8, 2015
#3
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Total playing time for all 30 is    30*42 = 1260 minutes

Total playing time for 25 left is  $${\mathtt{25}}{\mathtt{\,\times\,}}{\mathtt{42.8}} = {\mathtt{1\,070}}$$

Total playing time for the 5 gone is    $${\mathtt{1\,260}}{\mathtt{\,-\,}}{\mathtt{1\,070}} = {\mathtt{190}}$$

Average playing time for the 5 is      $${\frac{{\mathtt{190}}}{{\mathtt{5}}}} = {\mathtt{38}}$$     minutes

May 8, 2015