Question

A scientist wants an 81milliliter of saline solution with a concentration of 5% she has concentrations of 3% and 9%. How much of each solution must she use to get the desired concentration

Answer 1

The quantity of each concentrations of 3% and 9% needed to get the desired concentration is 54 milliliters and 27 milliliters respectively

Simultaneous equation

Let

• Quantity of 3% needed = x
• Quantity of 9% needed = y

x + y = 81

0.03x + 0.09y = 81 × 5%

0.03x + 0.09y = 4.05

x + y = 81

0.03x + 0.09y = 4.05

From (1)

x = 81 - y

• Substitute into

0.03x + 0.09y = 4.05

0.03(81 - y) + 0.09y = 4.05

2.43 - 0.03y + 0.09y = 4.05

- 0.03y + 0.09y = 4.05 - 2.43

0.06y = 1.62

y = 1.62/0.06

y = 27

• substitute y = 27 into

x = 81 - y

x = 81 - 27

x = 54

Simultaneous equation:

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