The rice sold by a grocer contained 20% of low-quality rice. What quantity of good-quality rice should be added to 175 kg of mixed rice so that the percentage of low-quality rice remains 10%?

Initial quantity of mixed rice = 175kg
Percentage of low-quality rice initially = 20%

Weight of low-quality rice initially = 175×
100
20
​
=35kg

Let the amount of good-quality rice to be added be xkg.
The total weight of the new mixture becomes (175+x)kg.

Since only good-quality rice is added, the quantity of low-quality rice remains unchanged at 35kg, which now constitutes 10% of the new mixture.

100
10
​
×(175+x)=35
175+x=350
x=350−175=175kg
Therefore, 175kg of good-quality rice should be added.