How many milliliters of a 2000.0 mg/dl stock solution are needed to prepare 100.0 ml of a 150.0 mg/dl working solution?

I answered one of your dilution/solution questions for you. I expect to see some work before I help with the others.

2000/100=150/x =7.5 ml?

That looks ok to me.

To determine the amount of a stock solution needed to prepare a working solution, we can use the equation:

C1V1 = C2V2

Where:
C1 = concentration of the stock solution
V1 = volume of the stock solution needed
C2 = concentration of the working solution
V2 = volume of the working solution desired

In this case, let's plug in the given values:

C1 = 2000.0 mg/dl
V1 = ?
C2 = 150.0 mg/dl
V2 = 100.0 ml

We can rearrange the equation to solve for V1:

V1 = (C2 * V2) / C1

Now let's substitute the given values into the equation:

V1 = (150.0 mg/dl * 100.0 ml) / 2000.0 mg/dl

V1 = 7.5 ml

Therefore, 7.5 milliliters of the 2000.0 mg/dl stock solution are needed to prepare 100.0 ml of a 150.0 mg/dl working solution.