Question 227860
the formula for for y varies directly with x is:


y = k*x


when y = 65, x = 5, so your equation becomes:


65 = 5*k


solve for k and you get k = 13 because 13 * 5 = 65.


question was find y when x = 12.


equation of y = k*x becomes y = 13 * 12 = 156.


you have y = 156 when x = 13.


we solved this using the formula y = k*x.


we could also have solved this by using the ratio equation of:


5/65 = 12/y


cross multiply to get 5*y = 12*65


divide both sides of this equation by 5 to get:


y = 12*65/5 which becomes y = 12*13 which becomes y = 156


This website has the formulas for variation that you would need.


<a href = "http://www.purplemath.com/modules/variatn.htm" target = "_blank">Direct and Inverse Variation Formulas plus Others</a>