Numsprite數靈精Play free
中文

Maths olympiad question · P2–P4★★ Medium

Cycles: olympiad question 4

A medium question on cycles for P2–P4, with a step-by-step solution, diagrams and the answer. Cycle questions appear in the Hua Xia Cup from the P1 first round to the P5 papers: which comes in a given place, which day of the week, which last digit.

The question

May threads beads for a bracelet, repeating the pattern "1 red, 1 white" over and over.

She threads 23 beads in all.

How many of the beads are white?

Show the hints (2)
  1. Hint 1: How many beads make a group, and how many of those are white?
  2. Hint 2: Beads left over after the whole groups — check one by one whether each is red or white.

Worked solution

Have a go first, then read the solution step by step.

  1. 1.A group is 1 + 1 = 2 beads, 1 of them white. 23 ÷ 2 = 11 remainder 1.
  2. 2.11 groups hold 11 × 1 = 11 white beads.
  3. 3.1 bead left over: each group starts with red, so the first 1 is red. White beads: 11 + 0 = 11.
  4. ⚠️Common mistake: counting all the left-over beads as white, or ignoring them.

Answer: 11 beads

Play more like this in Numsprite (unlimited questions, instant marking) →A free maths game: every level free from Easy to Expert (★ to ★★★★), unlimited questions, no download