=+13. The article “Ecological Determinants of Herd Size in the Thorncraft’s Giraffe of Zambia” (Afric. J. Ecol., 2010: 962–971) gave the following data (read from a graph) on herd size for a sample of 1570 herds over a 34-year period.

Herd size: 1 2 3 4 5 6 7 8 Frequency: 589 190 176 157 115 89 57 55 Herd size: 9 10 11 12 13 14 15 17 Frequency: 33 31 22 10 4 10 11 5 Herd size: 18 19 20 22 23 24 26 32 Frequency: 2 4 2 2 2 2 1 1