A Chemist has 100g of 25% acid solution. How much of these solution he needs to drain and replaced with 70% acid solution to obtain 100g of 60% acid solution?

this can be solved by establishing system of eqution:

let x be the amount of 25 % acid soln needs to be drained

y is the amount of 70% acid solution

first equation:

(100 - x) + y = 100

Second equation

0.25 (100 - x) + 0.7y = 0.60 (100)

Solving the system of equation

X = 77.78 g of 25 % acid solution is needed to be drained