Question 1190461
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b = number of blue shirts
r = number of red shirts
d = cost of buying b blue shirts


b blue shirts cost d dollars
1 blue shirt costs d/b dollars. I divided both parts by b.


Example:
b = 4, d = 8
4 blue shirts cost 8 dollars
1 blue shirt costs 8/4 = 2 dollars



1 blue shirt is 1/5 the cost of 1 red shirt
Phrased in reverse, 1 red shirt is 5 times the cost of 1 blue shirt.


So,
cost of 1 red shirt = 5*(cost of 1 blue shirt)
cost of 1 red shirt = 5*(d/b)
cost of 1 red shirt = (5d)/b


The last step is to multiply that expression by r to find the cost of buying r number of red shirts.
We go from (5d)/b to (5rd)/b


Answer: <font color=red>(5rd)/b  which is choice (d)</font> 
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