Crown-Rump Length. In the article “Fetal Crown Length:

Re-evaluation of relation to menstrual age with high- resolution realtime Ultra-Sound.” (Radiology, Vol. 182, Issue 2), F. P. Hadlock et al. evaluated the relationship between crown-rump length and menstrual age of fetuses in a population of 416 patients. The following table shows the length of crown-rump (x), in millimetres, and age of foetuses (y), in weeks. For part (g), predict the age of the fetus for 90 mm crown-rump length.

x 2 20 40 60 80 100 120 y 5.7 8.6 10.9 12.5 14.0 15.9 17.9