Question

Describe how you would prepare 125 ml of a 0.8% w/v agarose in 1X TAE buffer starting with a 20X TAE stock solution and solid agarose powder.

Answer 1

You will need to count how much TAE buffer you need. The buffer volume needed would be:
buffer1 * volume1 = buffer2 * volume2
1* 125ml= 20 * volume2
volue2= 125ml/20= 6.25ml

Add the 6.25ml buffer, then add the agarose.
Since the agarose is powder, you need to weight the amount of agarose needed. The calculation would be: 
weight = volume * density * pencentage
weight = 125 ml * 1g/ml * 0.8%= 1g

After that, you can add water the solution until the volume is 125ml. The amount needed would be around: 125ml-6.25ml= 118.75 ml