Three boxes B1,B2,B3 are selected with probabilities 0.40,0.35,0.25 respectively. The probabilities of drawing a blue ball from these boxes are 0.10,0.20,0.25 respectively. Which of the following expressions equals the probability that a ball drawn at random is blue?
a) 0.40×0.10+0.35×0.20
b) 0.40×0.10+0.35×0.20+0.25×0.25
c) 30.10+0.20+0.25
d) 0.40×0.20+0.35×0.25+0.25×0.10