To determine the possible combinations of board books and soft-covered books that total $20, you'd typically start with a cost equation based on the prices of each book type. For example, if board books cost $1 each and soft-covered books cost $0.50 each, the equation would look like this:
Let:
- \( b \) = number of board books
- \( s \) = number of soft-covered books
Then the equation would be: \[ 1b + 0.5s = 20 \] or, multiplying everything by 2 to eliminate the decimal: \[ 2b + s = 40 \]
To find positive integer combinations of \( b \) and \( s \), we can rearrange this equation: \[ s = 40 - 2b \]
Now we can find combinations by plugging in integer values for \( b \):
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For \( b = 0 \): \[ s = 40 - 2(0) = 40 \] Combination: \( (0, 40) \)
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For \( b = 1 \): \[ s = 40 - 2(1) = 38 \] Combination: \( (1, 38) \)
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For \( b = 2 \): \[ s = 40 - 2(2) = 36 \] Combination: \( (2, 36) \)
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For \( b = 3 \): \[ s = 40 - 2(3) = 34 \] Combination: \( (3, 34) \)
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For \( b = 4 \): \[ s = 40 - 2(4) = 32 \] Combination: \( (4, 32) \)
Continue this pattern until \( b \) is such that \( s \) remains non-negative. Here are three more combinations:
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For \( b = 5 \): \[ s = 40 - 2(5) = 30 \] Combination: \( (5, 30) \)
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For \( b = 6 \): \[ s = 40 - 2(6) = 28 \] Combination: \( (6, 28) \)
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For \( b = 7 \): \[ s = 40 - 2(7) = 26 \] Combination: \( (7, 26) \)
Continuing with this pattern, the last combinations will be:
- \( (15, 10) \)
- \( (20, 0) \)
From your provided options, these combinations can be summarized as:
- 0 board books and 40 soft cover books
- 1 board book and 38 soft cover books
- 2 board books and 36 soft cover books
- 3 board books and 34 soft cover books
- ... up until 15 board books and 0 soft cover books.
However, it looks like the provided combinations do not match all possible equations. Please verify the prices of each book to get accurate combinations.
If you can clarify what the cost of each book type is, we can provide the exact combinations that add up to $20.