The cost price of 30 article in the same as the selling price x articles.If the profit is 25%, then the value of x is:

Given, 

Cost price of 30 articles = selling price of x articles 

$$30\times\ CP=x\times\ SP$$

$$\therefore\ \frac{SP}{CP}=\frac{30}{x}$$.........(i)

Profit % = $$\frac{SP-CP}{CP}\times\ 100\ =\ 25$$ (given)

$$\frac{SP}{CP}-1=\ \frac{25}{100}$$

$$\frac{SP}{CP}=\ \frac{1}{4}+1$$

$$\frac{SP}{CP}=\ \frac{5}{4}$$..........(ii)

Equating (i) and (ii) , we get

$$\frac{30}{x}=\ \frac{5}{4}$$

$$x=24$$

Hence, option C is correct.