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# Dexter found 288 shells in his first four visits to the beach and 405

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Dexter found 288 shells in his first four visits to the beach and 405  [#permalink]

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12 May 2017, 04:10
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Difficulty:

15% (low)

Question Stats:

88% (01:17) correct 12% (02:11) wrong based on 29 sessions

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Dexter found 288 shells in his first four visits to the beach and 405 shells in his next five visits. What is the average (arithmetic mean) number of shells he found per visit?

A. 81
B. 77
C. 72
D. 45
E. 32

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Re: Dexter found 288 shells in his first four visits to the beach and 405  [#permalink]

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12 May 2017, 04:45
1
288+405=693 shells in total
693/9 visits= 77 shells per visit
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Re: Dexter found 288 shells in his first four visits to the beach and 405  [#permalink]

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12 May 2017, 06:48
1
Top Contributor
Bunuel wrote:
Dexter found 288 shells in his first four visits to the beach and 405 shells in his next five visits. What is the average (arithmetic mean) number of shells he found per visit?

A. 81
B. 77
C. 72
D. 45
E. 32

TOTAL # of shells collected = 288 + 405 = 693
TOTAL # of visits = 4 + 5 = 9

So, AVERAGE # of shells per visit = 693/9

ASIDE: We can avoid performing this calculation if we focus on the units digits

If AVERAGE # of shells per visit = 693/9, we can also say: (AVERAGE # of shells per visit)(9) = 693

So, among the answer choices, we're looking for one such: (the units digit)(9) = --3
Only one answer choice (77) works.

Since (7)(9) = 63, we know that the correct answer is 77

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Re: Dexter found 288 shells in his first four visits to the beach and 405  [#permalink]

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16 May 2017, 17:22
1
Bunuel wrote:
Dexter found 288 shells in his first four visits to the beach and 405 shells in his next five visits. What is the average (arithmetic mean) number of shells he found per visit?

A. 81
B. 77
C. 72
D. 45
E. 32

We are given that Dexter found a total of 288 shells in his first 4 visits and a total of 405 in his next 5 visits. So he found a total of 288 + 405 = 693 shells in a total of 9 visits.

Thus, the average number of shells that Dexter found per visit was 693/9 = 77 shells.

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Re: Dexter found 288 shells in his first four visits to the beach and 405  [#permalink]

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17 May 2017, 02:35
Dexter found 288 shells in his first four visits to the beach and 405 shells in his next five visits. What is the average (arithmetic mean) number of shells he found per visit?
A. 81
B. 77
C. 72
D. 45
E. 32

Average number of shells = Total number of shells / Total number of visits to beach
Total number of shells = 288 + 405 = 693
Total number of visits to beach = 9
Therefore Required Average = $$\frac{693}{9}$$ = 77

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Re: Dexter found 288 shells in his first four visits to the beach and 405  [#permalink]

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17 May 2017, 12:05
easy calculation method:
average on the first four days is 288 divided by 4, ie 72
average on the next five days is 405 divided by 5, ie 81

Now, the average over the 9 days is: Average = (72*4 + 81*5) / 9 --- Tip: 72 divided by 9 gives 8 and 81 divided by 9 gives 9
Therefore: Average = 8*4 + 9*5 = 32 + 45 = 77
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Re: Dexter found 288 shells in his first four visits to the beach and 405 &nbs [#permalink] 17 May 2017, 12:05
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