Question 147693
( 20 * 10% + x * 100% ) / ( 20 + x ) = 25%
( 20 * 0.1 + x ) / ( 20 + x ) = 0.25
( 2 + x ) / ( 20 + x ) = 0.25
2 + x = 0.25( 20 + x )
2 + x = 5 + 0.25x
0.75x = 3
x = 4kg salt