The figure below represenis a certain race alono a siraighL course. The race staited at S and finished at F. A certain runner parlicipaiino in Ihis race clocked elapsed times r rg. fc. ID, and rF minutes from S 10 poinis A, B, C. D, and F, ielpecijirely. If BC. for example, denoies the disiance beEween poinis B and C, and all distances are measured in kilometers, which of Ihe followino expressions necessarily represenis ihe runner's aK'erage speed for this race, in kilomeiers per minute? elapsed lime SA SB sc SD SF rF ACT-SS 20 GO ON TO THE NEXT PAGE.
