In 2 kg mixture of copper and aluminium, 30% is copper. How much aluminium powder should be added to the mixture so that the quantity of copper becomes 20% ?

According to the question,
Mixture of copper and aluminium = 2000 gms
30% copper = $$\frac{30}{100}$$ × 2000 = 600 gms
Aluminium in mixture = 2000 - 600 = 1400gm
Now 'x' weight of mixture have and 600 gm copper become 20% of its total weight.
i.e. x = $$\frac{{600}}{{20}} \times 100 $$   = 3000gm
Total amount of Aluminium in mixture = 3000 - 600 = 2400
Additional aluminium powder added = 2400 - 1400 = 1000gm