Question 1089172
Normally usage is some Q units of cooking oil.


Increased cost {{{1.15cross(Q)}}}
Cost wanted,  {{{1.00*cross(Q)}}}


x, fraction of 1.00Q cost 
{{{1.15Qx=1.00Q}}}
{{{1.15x=1}}}
{{{x=1/1.15}}}


{{{x=0.870}}}

Family should use 87% of the oil that they had used now that the price increased, to keep the expenditure the same.