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A tank contains 200 fish and 99% of them are tetras. How many tetras should be removed so that exactly 98% of the fish in the tank are tetras?

 Nov 5, 2019
 #1
avatar+19937 
+2

200 (.99)    number of tetras originally    now subtrac x from that number

200(.99) - x       the TOTAL number of fish also gets decreases to 200 - x

 

The tetras remaining in the tank   200(.99) - x

    divided by the total number of fish  200- x   = 98 %

 

[200(.99) - x ] / (200-x) = .98     solve for 'x' the number of tetras to remove....  

 Nov 5, 2019
 #2
avatar+105238 
+1

If 99%  are tetras.....then  .99 * 200  =  198 are tetras  

Let N be the number of tetras to be removed....so

 

[ 198 - N  ] / [ 200 - N ]  =  .98      cross-multiply

 

198 - N  =  .98 [ 200 - N ]

 

198 - N =  196 - .98N        Add N to both sides......subtract 196 from both sides

 

2  =  .02N                     Divide both sides by  .02

 

100 = N  =  the number to be removed

 

Proof

 

[ 198 - 100 ] / [ 200 - 100]  =

 

98 / 100   =   .98  = 98%

 

 

cool cool cool

 Nov 5, 2019

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