Can you form a triangle?
A box contains 7 rods measuring 15 cm, 15 cm, 30 cm, 40 cm, 60 cm, 60 cm and 90 cm.
THREE of theses rods are randomly chosen.
What is the probability that they can be arranged to form a triangle?
The probability can be expressed as a/b for co-prime positive integers a and b, find the value of a+b.