1. There is a chain made of red, white and black beads in the order of five red, four white and three black beads, sharing 185 beads. How many are the black beads? What color is the 69th?

1. There is a chain made of red, white and black beads in the order of five red, four white and three black beads, sharing 185 beads. How many are the black beads? What color is the 69th?

Red + white + Black = 5 + 4 + 3 = 12, that is, 12 beads are a cycle
185 = 12 * 15 + 5, namely 15 groups (5 Red + 4 white + 3 Black) plus 5 red
So the number of black beads:
15 * 3 = 45;
69th bead:
69 = 12 * 5 + 9, that is, 5 circulation groups plus 9 beads, which are in the order of 5 red and 4 white, so they are white

What's the formula of unit 7 [mathematics wide angle] in Volume 1 of grade 6?

(total feet chicken feet * head) / (rabbit feet chicken feet) = rabbit number
(rabbit feet * head total feet) / (rabbit feet chicken feet) = chicken number

There are four people in the room. What's the probability that at least two people's birthdays are in the same month?

Suppose that at least two people's birthdays are in the same month as event a, then. A means that none of the four people's birthdays are in the same month, P (. A) = a412124 = 5596. According to the probability of opposite events, P (a) = 1-5596 = 4196