Question

Liters of 10% acid solution and liters of 70% acid solution

Answer 1

Let

x -----> number of liters of 10% acid solution

y ----> number of liters of 70% acid solution

so

we have that

x+y=90 ------> x=90-y -----> equation 1

Remember that

10%=10/100=0.10

70%=70/100=0.70

20%=20/100=0.20

so

0.10x+0.70y=0.20(90) ------> equation 2

Solve the system of equations

substitute equation 1 in equation 2

0.10(90-y)+0.70y=0.20(90)

solve for y

9-0.10y+0.70y=18

0.60y=18-9

0.60y=9

y=15

Find out the value of x

x=90-y

x=90-15=75

therefore

the answer is

number of liters of 10% acid solution is 75 and number of liters of 70% acid solution is 15