find the pair of linear equations and then solve them

Let x litres of 1st solution is taken.

and y litres of 2nd solution is taken.

Since, 10 litres of new solution is to be made, thus, first linear equation will be :

x + y = 10.

Now, 1st solution has 50% acid and 2nd solution has 25% acid. new solution has to be 40% acidic.

Thus, 2nd linear equation will be:

50% of x + 25% of y = 40% of 10

x/2 +y/4 = 4.

so, the 2 linear equations formed are:

x+y = 10

x/2 +y/4 = 4

solving for x and y, we get x= 6 and y = 4

so, we have to use 6 litres of 1st solution and 4 litres of 2nd solution to make the new solution.