Question 980078
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To place three paintings of equal width on a wall with
equal gaps between each painting and equal spaces on 
each end (between the other walls and end paintings):
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To get available space for gaps, we subtract total of painting
widths from total wall length. Since there are a total of 
four gaps, (one at each end and two between paintings), 
we divide by 4 to find length of each gap.
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Let L=length of wall; W=width of painting; G=gap
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G=(L-3W)/4