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# help

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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
+19963
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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
+106539
+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%

Nov 5, 2019