A scientist needs 10 L of a solution that is 60% acid. She has a 50% acid solution and a 90% acid solution she can mix together to make the 60% solution. Let x represent the number of liters of the 50% solution. Let y represent the number of liters of the 90% solution. Which equation represents the total liters of acid that are needed?
x + y = 6
x + y = 10
0.5x + 0.9y = 6
0.5x + 0.9y = 104

A scientist needs 10 L of a solution that is 60% acid
She has a 50% acid solution and a 90% acid solution she can mix together to make the 60% solution
x represents the number of liters of the 50% solution
y represents the number of liters of the 90% solution

We need to find the equation which represents the total liters of acid that are needed

∵ x represent the number of liters of the 50% solution

∴ The quantity of acid from the 50% solution = 50% × x

∵ 50% = 50 ÷ 100 = 0.5

∴ The quantity of acid from the 50% solution = 0.5 x liters

∵ y represents the number of liters of the 90% solution

∴ The quantity of acid from the 90% solution = 90% × y

∵ 90% = 90 ÷ 100 = 0.9

∴ The quantity of acid from the 90% solution = 0.9 y liters

∵ The scientist needs 10 L of a solution that is 60% acid

∴ The quantity of acid that she need = 60% × 10

∵ 60% = 60 ÷ 100 = 0.6

∴ The quantity of acid that she need = 0.6 × 10 = 6 liters

To find the total liters of acid add 0.5 x and 0.9 y and equate

the sum by 6

∵ The total amount of the acid = 0.5 x + 0.9 y liters

∵ The total liters of the acid is 6 liters

∴ 0.5 x + 0.9 y = 6

The equation that represents the total liters of acid that are needed is 0.5 x + 0.9 y = 6

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