[tex] \sf= \frac{100}{100 + 25} \times 4000 \\ = \frac{100}{125} \times 4000 \\ = \frac{4}{5} \times 4000 \\ = 4 \times 800 \\ = 3200[/tex]
[tex] \huge \sf \: Answer[/tex]
The cost price is 3200.
Hope you could get an idea from here
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