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Bunuel Why is the answer marked as B?
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Statement 1 is NOT sufficient , because there may be a wide variation in bill amounts: imagine two customers with bills of 90 each (15% tip) and three with bills of 20 dollars each (20% tip)

Tips 13.5 ,13.5 ,4,4,4 that sum to 39
Average tip 39/5 - less than 8 dollars

The key variable is how total bill dollars are distributed, not just what percent of the customers chose each tip.
Are we averaging people or dollars?
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Hi kevincan, can you please explain how to approach Statement 1 mathematically? I tried one example, and example I took was satisfying the condition, now looking at the example you have given, I can see we cannot be sure with Statement 1. So it would be good if we try to solve mathematically, will you be able to help? Thanks in advance :)
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Hi gullyboy09 let me try to help

Given

The average bill is $48 per customer. The tip rate for any individual is either 15% or 20%.

Let B be the Total Bill, T be the Total Tip, and N be the Number of Customers.

We know B / N = 48, which means
B= 48N.

The question asks: Is T / N > 8?

Since N=B/48

Then is T/B/48>8 T/B>1/6

Is the total tip pool strictly greater than 16.67% of the total bill pool?

Lets check Statement 1

Most of yesterday’s customers chose to leave a 20% tip

Let's test this with 3 customers whose average bill is $48 (Total Bill = $144)

Case A (Large bills and small tips)

Customer 1 (Bill: $140) leaves 15% tip = $21.00
​Customer 2 (Bill: $2) leaves 20% tip = $0.40
​Customer 3 (Bill: $2) leaves 20% tip = $0.40
​Most (2 out of 3) left a 20% tip.

Total Tip = $21.80.

Average Tip = $21.80 / 3 = $7.27 Is it > $8? NO

​Case B (Large bills n left large tips)

​Customer 1 (Bill: $2) leaves 15% tip = $0.30
​Customer 2 (Bill: $71) leaves 20% tip = $14.20
​Customer 3 (Bill: $71) leaves 20% tip = $14.20

​Most left a 20% tip. * Total Tip = $28.70. Average Tip = $28.70 / 3 = $9.56

Is it > $8? YES
​Because we get both a YES and a NO, Statement (1) is INSUFFICIENT.

gullyboy09
Hi kevincan, can you please explain how to approach Statement 1 mathematically? I tried one example, and example I took was satisfying the condition, now looking at the example you have given, I can see we cannot be sure with Statement 1. So it would be good if we try to solve mathematically, will you be able to help? Thanks in advance :)
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