19. A group of 40 boys and 28 girls stand hand in hand in a circle facing inwards. Exactly 18 of the boys give their right hand to a girl. How many boys give their left hand to a girl?
A 12
B 14
C 18
D 20
E 22
SOLUTION
C

We are told that 18 boys give their right hand to a girl and that there are 40 boys in the circle in total. Therefore 22 boys give their right hand to a boy. Since all the children are facing inwards, this means that all the boys who have a boy giving them their right hand, will in return be giving a boy their left hand. Hence 22 boys give their left hand to a boy. Therefore there will be 18 boys who give their left hand to a girl.