A 150 ml bottle of shampoo cost $3.85. What is the cost of a 100 ml bottle of shampoo?

First of all, you need to calculate a 300ml bottle of shampoo, because it will be easier. 3.85 x 2=$7.70 Now you use $7.70 and divided by 3. 7.70/3 = $2.60 (rounded up).

Therefore, a 100ml bottle of shampoo costs $2.60.