Question

In 1 kg mixture of sand and iron, 20% is iron. How much sand should be added, so that the proportion of iron becomes 5%?

• A. 3 kg
• B. 4 gm
• C. 5 gm
• D. 6 gm
• E. None of these

Answer 1

The correct option is A 3 kg

Here, in 1 kg of mixture.
Quantity of Iron $=1000\times \frac{20}{100}=200gm$
Now, $\frac{200}{1000+x}\times 100=5$
or 2000=5000+5x
or 15000=5x
or x=3000 g =3kg
Alternate Method
In these type of quesitons, percentage value and quantity of mixture are increased or decreased in the same proportion.
Percentage value =20%
=20% +4 =5%
Quantity =1kg $=1\times 4=4kg$
$\therefore$ Quantity added =4 -1 =3 kg