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findingmyself
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A convenience store currently stocks 48 bottles of mineral water. The 10 May 2025, 05:58
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For beginners: using this method:

X be the number of 20 Ltr bottles and Y be the number of 40 Ltr bottles

(20X+40Y)/48=35
20X+40Y= 48*35

Let 'a' be the number of bottles which needs to be removed to get the new average of 25

The new average equation is (20X+40(Y-A))/(48-A)=25

20X+40Y-40A=25*48-25A (Substitute 20X+40Y as 48*35 from above equation)
From this A=32

dred
A convenience store currently stocks 48 bottles of mineral water. The bottles have two sizes of either 20 or 40 ounces each. The average volume per bottle the store currently has in stock is 35 ounces. How many 40 ounce bottles must be sold for the average volume per bottle to be reduced to 25 ounces if no 20 ounce bottles are sold?

(A) 10
(B) 20
(C) 30
(D) 32
(E) 34
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shubhim20
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A convenience store currently stocks 48 bottles of mineral water. The 02 Jun 2025, 23:37
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Why are we including 20x when we only have to calculate with 40z and why not 40y?
ArvGMAT
32

Here is how I got it:

Average is 35 ounces
x is # of 20 ounce bottles
y is # of 40 ounce bottles

20x+40y/x+y = 35
solve to get y=3x

x+y=48 bottles
x=12, y=36

20x+40z/x+z=25

plug x=12 and solve for z, we get z = 4

So, y-z is # of bottles sold i.e 36-4 = 32
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Feb2024
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A convenience store currently stocks 48 bottles of mineral water. The 10 Jun 2025, 11:24
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Similar question from different source for practice:

https://gmatclub.com/forum/tourist-purc ... 37906.html
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Eshan12567
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A convenience store currently stocks 48 bottles of mineral water. The 15 Oct 2025, 18:16
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Given:
  • Total bottles = 48
  • Two sizes: 20 oz and 40 oz
  • Average volume = 35 oz
Let:
  • Number of 20 oz bottles = ( x )
  • Number of 40 oz bottles = ( y )
So,
x + y = 48
[hr]
Step 1: Use the average formula
Average = (Total volume) ÷ (Total bottles)
(20x + 40y)/48 = 35
20x + 40y = 1680
Divide everything by 20:
x + 2y = 84
We also know (x + y = 48).
Subtract the first from the second:
(x + 2y) - (x + y) = 84 - 48
y = 36
Then (x = 48 - 36 = 12).
✅ So initially:
  • 12 bottles are 20 oz
  • 36 bottles are 40 oz


Step 3: Selling 40-ounce bottles
Let the number of 40-ounce bottles sold = ( s ).
After selling:
  • 20 oz bottles = 12 (unchanged)
  • 40 oz bottles = ( 36 - s )
  • Total bottles = ( 48 - s )
Total volume left:
20(12) + 40(36 - s) = 240 + 1440 - 40s = 1680 - 40s


Step 3: Solve for ( s )
Multiply both sides by (48 - s)

1680 - 40s = 25(48 - s)

Simplify the right side:
1680 - 40s = 1200 - 25s
1680 - 1200 = 40s - 25s
480 = 15s
s = 32
Final Answer: 32 bottles
[hr]
✅ Meaning:
The store must sell 32 of the 40-ounce bottles to reduce the average volume per bottle from 35 oz to 25 oz.

dred
A convenience store currently stocks 48 bottles of mineral water. The bottles have two sizes of either 20 or 40 ounces each. The average volume per bottle the store currently has in stock is 35 ounces. How many 40 ounce bottles must be sold for the average volume per bottle to be reduced to 25 ounces if no 20 ounce bottles are sold?

(A) 10
(B) 20
(C) 30
(D) 32
(E) 34
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