5. An engineer designs an improved light bulb. The previous design had an
average lifetime of 1200 hours. The new bulb has a lifetime of 1201 hours,
using a sample of 2000 bulbs. Although the difference is quite small, the cffect
is statistically significant. The explanation is
(A)that new designs typically have more variability than standard designs.
(B) that the sample size is very large.
(C)that the mean of 1200 is large.
(D)all of the above.
【非選題】 3.(8 分) Let T(x, y, z) = 20 + 2x + 2y +Z2 represent the temperature
at each point on the sphere x2 + y2 +Z2 = 11. Calculate the mini-
mum and maximum temperatures on the curve formed by the inter-
section of the plane x + y + z = 3 and this sphere.