How to dilute alcohol level 99% to 70 %

If you have 99% alcohol you can dilute to 70% or any percent you want here's the formula

Formula:
c1 X v1 = c2 X v2

Legends:
c1 = your existing alcohol level that you wan to dilute
v1 = volume of your existing alcohol in ml (sample 500ml)
c2 = your target alcohol level (sample 70% , 40%)
v2 = total volume

TO GET THE VOLUME OF WATER TO BE ADDED V2 - V1 (Subtract the TOTAL VOLUME to Volume of existing alcohol )

SAMPLE COMPUTATION
you have 100ml of 99.9% alcohol and you want to dilute to 40%
c1= 99.9
v1= 100
c2= 40
v2 = ?

applying to equation
c1 X v1 = c2 X v2
99.9 X 100 = 40 X v2?
by using mathematical equation divide both by 40, therefore
99.9 X100 / 40 = v2?

Re arrange the equation
v2? = 99.9 X 100 / 40
v2? = 9,990 / 40
v2? = 249.8
249.8 = this will be the TOTAL of our alcohol diluted to 40%

To get the actual volume of distilled water to be add, subtract the TOTAL VOLUME to the EXISTING ALCOHOL before you dilute (v2 - v1)
v2 = 249.8
v1 = 100
therefore
249.8 - 100 = 149.8

Conclusion:
To be able to dilute a 100ml of 99.9 alcohol to 40% alcohol level,you need to add 149.8 ml of water