17. The football shown is made by sewing together 12 black pentagonal panels and 20 white hexagonal panels. There is a join wherever two panels meet along an edge.
How many joins are there?

A 20
B 32
C 60
D 90
E 180
17. D The 12 pentagonal panels have a total of $12 \times 5=60$ edges. The 20 hexagonal panels have a total of $20 \times 6=120$ edges. So in total the panels have 180 edges. When the panels are sewn together, two edges form each join. So the number of joins is $180 \div 2=90$.