Ac=d-r, solve for a
help please

Heather is riding a quadratic function that represents a parabola that touches but does not cross the x-axis at x=-6

1. according to the internal revenue service, the mean tax refund for the year 2007 was $2,708. assume the standard deviation is $650 and that the amounts refunded follow a normal probability distribution. a. what percent of the refunds are more than $3,000? b. what percent of the refunds are more than $3,000 but less than $4,000? c. what percent of the refunds are less than $2,000?

Why is causation so much more difficult to prove than correlation?