If the price of rice increases by 20% and Aling Petra intends to spend only 5% more on rice, by how much percent should she reduce the quantity of rice that she buys? Can anyone describe the process?

Question

anonymous · Answer

i have an idea

anonymous · Answer

since we don't know how much rice cost, and since it clearly doesn't matter for the problem, pick a number

anonymous · Answer

say it cost a dollar.  then if it increases by 20% it now cost $1.20

anonymous · Answer

and since you are only going to spend 5% more you are going to spend $1.05

anonymous · Answer

yeah, but how do I know the quantity reduced in percent? Thanks!

anonymous · Answer

so how much rice can you buy for $1.05? well you can only buy 
$$\frac{1.05}{1.20}$$ of the rice you used to by.  this is .875 or if you prefer 87.5%

anonymous · Answer

meaning you buy 
$$100-87.5=12.5\%$$ less

anonymous · Answer

Thanks! You rock.