Goal Seek on multiple cells (HELP)

[afzalzada]

So, I'm working in a telecom company in Postpaid section, we have recently changed our billing system and now we are facing problem with setting limits to customers.
for example : a customer requests us to set his monthly limit to 500. while entering the 500 in the limit area, the system allocates the limit in the below format { 500*10%(10% telecom tax) - 400(two months rental) } thus the system will only allow 50 limit per month for the number. [ 500*10%-400 = 50 ].
my question is ( how to set the exact limit as per customer request i.e. 500 per month instead of 50. I could Achieve this by Goal Seek but it can't be applied to several cells and I have thousands of numbers. attached is an example.

[Crooza]

Your arithmetic seems to be a bit off but if I understand correctly you won't need goal seek, you can back calculate by taking the desired response adding 400 and dividing by 0.9 to get the 'manual override' figure to enter into the system

Eg.

Customer wants 500. 500 +400 = 900
900 /0.9 = 1000 so enter 1000 into the system to get a result of 500

Or customer wants 1200 so using the formula (1200 +400)/0.9 = 1778 (round up)

Is this what you're after?

[afzalzada]

Thanks for the great response, you saved my day. just want to know where did you get the (0.9)? thanks again

[Crooza]

You subtract 10 % for tax which is the same a leaving you with 90% or 0.9