Final answer:
The strongest correlation coefficient among the choices given is -0.9, which indicates a strong negative relationship between two variables.
Step-by-step explanation:
When evaluating the strength of a correlation between two variables, the correlation coefficient r is used. This value ranges from -1 to 1, with -1 indicating a perfect negative correlation, 1 indicating a perfect positive correlation, and 0 indicating no correlation. The absolute value of the correlation coefficient determines the strength of the relationship, regardless of the sign, which only indicates the direction (positive or negative) of the relationship.
In this question, the correlation coefficients given are +0.1, -0.7, +0.5, and -0.9. The coefficient that indicates the strongest relationship between two variables is -0.9, as it is closest to 1 in absolute value, which means it has the strongest correlation, even though it is negative. This high value indicates that as one variable increases, the other variable decreases in a highly predictable manner.