Problem 16 · 2014 Math Kangaroo
Medium
Counting & Probability
careful-countinggrid-counting
How many dots are in the picture?
Show answer
Answer: B — 181
Show hints
Hint 1 of 3
The pattern of dots is made of squares that share their edges, so some dots belong to more than one square.
Still stuck? Show hint 2 →
Hint 2 of 3
Count one row of dots at a time, going down the picture.
Still stuck? Show hint 3 →
Hint 3 of 3
When a dot sits where two squares meet, count it just once, then add all the rows up.
Show solution
Approach: systematic row-by-row dot count
- Sweep the picture in regular rows, tallying dots and avoiding counting shared corners twice.
- Summing the rows gives 181 dots in all.
- Answer: 181.
Mark:
· log in to save