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Solution
Only one question can be answered at a time. Hence it is Q 16 is being answered.
Let $ x be the cost per resident, originally. Also let the number of residents considered earlier be n. Now the revised cost is $ x+3 per resident and the number of residents being considered is n-225. Thus
nx= 1200000= (n-225)(x+3), as the total cost remains 1200000.
From nx= 1200000, n= 1200000/x; From (n-225)(x+3)= 1200000, it is nx-225x +3n-675= 1200000. In this equation substitute nx= 1200000 and n= 1200000/x, to get
1200000-225x +3 (1200000/x) -675= 1200000
Or, -225x + 3600000/x -675=0, Now multiply all terms by x,
-225x2 -675x +3600000=0
225x2 +675x- 3600000=0, Now divide all terms by 225,
x2 +3x -16000=0. , Now this quadratic can be factorised as follows:
x2 +128x -125x -16000=0
x(x+128)-125(x+128)=0
(x+128)(x -125)=0, Hence x= -128 or 125. Reject the negative value, hence x= 125
$125 was thus the original cost per resident. The revised cost is therefore $128.... Answer
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