# Whats the cost when: retail = cost + 10%

#### Bob58

##### New member
I'm new. Thanks for your patience. I need to know the formula for calculating the cost of an item. What i know is: Retail = Cost + 10%.
Example: Cost + 10% = 92.40.
I'm sure the formula is simple, but i graduated high school in 1972 and havent needed to know these types of formulas since.
Thank you
Bob

#### jwpaine

##### Full Member
Bob58 said:
I'm new. Thanks for your patience. I need to know the formula for calculating the cost of an item. What i know is: Retail = Cost + 10%.
Example: Cost + 10% = 92.40.
I'm sure the formula is simple, but i graduated high school in 1972 and havent needed to know these types of formulas since.
Thank you
Bob
I just had my wisdom teeth taken out, so I'm a little loopy right now.

10% of what? 10% of cost?

if so, then:

C + 0.1C = 92.40

1.1C = 92.40

1.1C/1.1 = 92.40/1.1

C = 84

See?

John.

#### Denis

##### Senior Member
Cost = retail / (1 + rate)

Cost = 92.40 / (1 + .10) = 92.40 / 1.10 = 84