Answer:
50mL of 8% solution
Step-by-step explanation:
Givens
Let the number of mL of 10% solution needed = x
Let the number of mL of 7% solution to be used = 100
She needs an 8% solution.
10%*x + 100*7% = (100 + x)*8%
(10/100)*x + 100*7/100 = 100*8/100 + x*8/100 Multiply through by 100
10x + 700 = 800 + 8x Subtract 700 from both sides
10x + 700 - 700 = 800 - 700 + 8x
10x = 100 + 8x Subtract 8x from both sides.
10x - 8x = 100 Combine like terms on the left
2x = 100 Divide by 2
x = 100/2 Do the division
x = 50
You need to add 50 Ml of the 10% solution.
Check
Left Hand Side
100 mL of 7% = 7 mL of active ingredient.
50 mL of 10% = 5 mL of active ingredient
Total 12 mL of active ingredient
Right Hand Side
150 mL of 8% = 12 mL of active ingredient
And it checks.
