A box contains a total of 56 balls of red and blue color in the ratio of 3: 5. What is the least number of red balls that should be removed from the box, such that the ratio of red and blue balls is less than 2 to 7?
a.9
b. 10
c.11
d.12
e.13
What is the easiest solution in this problem?
OA D
A box contains a total of 56 balls of red and blue color
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Hi lheiannie07,
We're told that a box contains a total of 56 balls of red and blue color in the ratio of 3:5. We're asked for the LEAST number of red balls that should be removed from the box, such that the ratio of red and blue balls is LESS than 2 to 7.
To start, we can determine the number of red and blue balls. Since the ratio is 3 red balls for every 5 blue balls, the total number of balls MUST be a multiple of (3+5) = 8. We're told that the total is 56, so that is seven 'groups' of 8 balls...
7(3) = 21 red balls
7(5) = 35 blue balls
Now we have to remove enough red balls that the new ratio of red balls to blue balls becomes LESS than 2:7. Notice that the current number of blue balls is 35 (which is a multiple of 7), so we can use the same math approach from before - but in reverse - to determine the number of red balls we'll need to keep)...
35 blue balls is five 'groups' of 7 blues balls
Five 'groups' of 2 red balls would be 10 red balls
So if we had 10 red balls and 35 blue balls, then the ratio of red to blue would be EXACTLY 2:7. We need it to be LESS than 2:7 though, so we would have to remove one additional red ball...
21 - 11 = 10 red balls - 1 = 9 red balls
Thus, we would have to remove 12 red balls.
Final Answer: D
GMAT assassins aren't born, they're made,
Rich
We're told that a box contains a total of 56 balls of red and blue color in the ratio of 3:5. We're asked for the LEAST number of red balls that should be removed from the box, such that the ratio of red and blue balls is LESS than 2 to 7.
To start, we can determine the number of red and blue balls. Since the ratio is 3 red balls for every 5 blue balls, the total number of balls MUST be a multiple of (3+5) = 8. We're told that the total is 56, so that is seven 'groups' of 8 balls...
7(3) = 21 red balls
7(5) = 35 blue balls
Now we have to remove enough red balls that the new ratio of red balls to blue balls becomes LESS than 2:7. Notice that the current number of blue balls is 35 (which is a multiple of 7), so we can use the same math approach from before - but in reverse - to determine the number of red balls we'll need to keep)...
35 blue balls is five 'groups' of 7 blues balls
Five 'groups' of 2 red balls would be 10 red balls
So if we had 10 red balls and 35 blue balls, then the ratio of red to blue would be EXACTLY 2:7. We need it to be LESS than 2:7 though, so we would have to remove one additional red ball...
21 - 11 = 10 red balls - 1 = 9 red balls
Thus, we would have to remove 12 red balls.
Final Answer: D
GMAT assassins aren't born, they're made,
Rich
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As Rich has shown, the box ORIGINALLY has 21 RED balls and 35 BLUE balls.lheiannie07 wrote:A box contains a total of 56 balls of red and blue color in the ratio of 3: 5. What is the least number of red balls that should be removed from the box, such that the ratio of red and blue balls is less than 2 to 7?
a.9
b. 10
c.11
d.12
e.13
Let x = number of RED balls to be removed from the box.
Once we remove x RED balls, there are 21-x RED balls and 35 BLUE balls.
We want the ratio of red and blue balls to be less than 2 to 7
So, we want: 21-x /35 < 2/7
Multiply both sides of the inequality by 35 to get: 21 - x < 70/7
Simplify: 21 - x < 10
Add x to both sides: 21 < 10 + x
Subtract 10 from both sides to get: 11 < x
If x must be GREATER THAN 11, then the smallest possible value of x is 12
Answer: D
Cheers,
Brent
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We an create the equation:lheiannie07 wrote:A box contains a total of 56 balls of red and blue color in the ratio of 3: 5. What is the least number of red balls that should be removed from the box, such that the ratio of red and blue balls is less than 2 to 7?
a.9
b. 10
c.11
d.12
e.13
3x + 5x = 56
8x = 56
x = 7
So there are 21 red balls and 35 blue balls. We can let n = the number of red balls to be removed and create the proportion:
(21 - n)/35 < 2/7
7(21 - n) < 70
147 - 7n < 70
77 < 7n
11 < n
The minimum value is 12.
Answer: D
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