Regression Estimate 2A1138
1. **State the problem:**
We are given the regression line equation $$y = -\frac{2}{3}x + \frac{125}{3}$$ which estimates IB Diploma points ($y$) based on hours spent on social media ($x$).
An eleventh girl spent 34 hours on social media, and we need to estimate her IB Diploma points using the regression line.
2. **Use the regression line formula:**
The formula to estimate $y$ given $x$ is:
$$y = -\frac{2}{3}x + \frac{125}{3}$$
3. **Calculate the estimate for $x=34$:**
Substitute $x=34$ into the equation:
$$y = -\frac{2}{3} \times 34 + \frac{125}{3}$$
Calculate each term:
$$-\frac{2}{3} \times 34 = -\frac{68}{3}$$
So,
$$y = -\frac{68}{3} + \frac{125}{3} = \frac{125 - 68}{3} = \frac{57}{3} = 19$$
Therefore, the estimated IB Diploma points for the girl who spent 34 hours on social media is **19 points**.
4. **Reason why this estimate is not reliable:**
The original data only includes students who spent between 3 and 30 hours on social media. The value $x=34$ is outside this range, so this estimate is an **extrapolation** beyond the observed data. Extrapolations can be unreliable because the linear relationship may not hold outside the observed range.
**Final answer:**
The estimated IB Diploma points for the girl who spent 34 hours on social media is **19 points**.
This estimate is not reliable because it is an extrapolation beyond the data range (3 to 30 hours).