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16 Sep 2014, 00:17
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For the past \(k\) days, Liv has baked an average (arithmetic mean) of 55 cupcakes per day. Today, Bibi helped Liv, and together they baked 100 cupcakes, raising the average to 60 cupcakes per day. What is the value of \(k\)?
A. 8
B. 9
C. 10
D. 12
E. 13
A. 8
B. 9
C. 10
D. 12
E. 13
16 Sep 2014, 00:17
Kudos
Bookmarks
Official Solution:
For the past \(k\) days, Liv has baked an average (arithmetic mean) of 55 cupcakes per day. Today, Bibi helped Liv, and together they baked 100 cupcakes, raising the average to 60 cupcakes per day. What is the value of \(k\)?
A. 8
B. 9
C. 10
D. 12
E. 13
The total number of cupcakes baked in \(k\) days was \(55k\), which means that the total number of cupcakes baked in \(k+1\) days was \(55k+100\). The new average is \(\frac{55k+100}{k+1} = 60\).
Thus, \(55k + 100 = 60k + 60\) and \(k = 8\).
Answer: A
For the past \(k\) days, Liv has baked an average (arithmetic mean) of 55 cupcakes per day. Today, Bibi helped Liv, and together they baked 100 cupcakes, raising the average to 60 cupcakes per day. What is the value of \(k\)?
A. 8
B. 9
C. 10
D. 12
E. 13
The total number of cupcakes baked in \(k\) days was \(55k\), which means that the total number of cupcakes baked in \(k+1\) days was \(55k+100\). The new average is \(\frac{55k+100}{k+1} = 60\).
Thus, \(55k + 100 = 60k + 60\) and \(k = 8\).
Answer: A
18 Mar 2015, 05:56
Kudos
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Hi,
I approached the prob in this way.
Average of 60 indicates that 5 more needs to be added in k days and 60 on the last day.
The question says 5k + 60 = 100
Therefore, k = 8
Posted from my mobile device
I approached the prob in this way.
Average of 60 indicates that 5 more needs to be added in k days and 60 on the last day.
The question says 5k + 60 = 100
Therefore, k = 8
Posted from my mobile device
