A mixture of petrol and kerosene weighing 5 kg contains 5% kerosene. How much more kerosene (approx.) must be added into it to make it 10%?

Initial amount of Kerosene(I) = 5% of 5 kg mixture of petrol and kerosene = $$\frac{5}{100}\times 5000 = 250$$ grams 

Let say 'x' gm of Kerosene is added to the mixture.

The final amount of Kerosene in the mixture after the addition is given as 10%.

$$\Rightarrow \frac{250 + x}{5000 + x} = \frac{10}{100}$$

$$\Rightarrow 2500 + 10x = 5000 + x$$

$$\Rightarrow 9x = 2500$$

$$\Rightarrow x = 275$$ gm approximately.

Therefore additionally 275 gm of kerosene is to be added to the mixture to make it 10%.