Encuentra el determinante ∆x del sistema 3 x 3 del siguiente problema: “Las edades de tres hermanas suman 68 años. El doble de la suma de las edades de las hermanas mediana y menor más la de la hermana mayor dan 109 años. Si la diferencia de edades entre la hermana mayor y la menor es de nueve años.” Nota: x= mayor, y = mediana, z = menor

The management of a supermarket wants to adopt a new promotional policy of giving a free gift to every customer who spends more than a certain amount per visit at this supermarket. the expectation of the management is that after this promotional policy is advertised, the expenditures for all customers at this supermarket will be normally distributed with a mean of $95 and a standard deviation of $20. if the management wants to give free gifts to at most 10% of the customers, what should the amount be above which a customer would receive a free gift?