# problem-10.20

problem-10.20 The output of summary() includes

    Coefficients:
                 Estimate Std. Error t value Pr(>|t|)
    (Intercept) -101.9075    23.2918   -4.38  1.4e-05 ***
    gestation      0.4503     0.0391   11.52  < 2e-16 ***
    age            0.1350     0.1881    0.72    0.473
    ht             1.2230     0.2852    4.29  2.1e-05 ***
    wt1            0.0308     0.0343    0.90    0.369
    dage           0.0603     0.1655    0.36    0.716
    dht           -0.0783     0.2706   -0.29    0.772
    dwt            0.0783     0.0331    2.37    0.018 *

So the coefficients for gestation, ht, and dwt are flagged.
The AIC choice is found with stepAIC()

    > library(MASS)                 # to load stepAIC
    > stepAIC(res.lm)
    ...
    Call:
    lm(formula = wt ~ gestation + age + ht + dwt, data = b)

    Coefficients:
    (Intercept)    gestation          age           ht          dwt
      -109.1946       0.4532       0.2156       1.3016       0.0756