A 15 oz bottle of shampoo lasts 10 weeks. If she buys an 18 oz bottle of the same brand, how long will it last her?

Question

I do not understand this word problem.  I have tried to solve it but i do not think I am getting the right answer.

Answer 1

problems of this type are solved by writing a PROPORTION.

 

15 oz / 10 weeks = 18 oz / x weeks

3/2 = 18/x  or 2/3 = x/18 (you can invert each side of any proportion.

 

now, after multiplying both sides by 18, you see that x = (2/3)(18); x =12 weeks.