Make 10 rows with 3 coins in each row, using only 9 coins.
Solution. Let’s take a closer look.
‘X’s represent the coins.
We’ve marked the first three rows in pink.
Fourth row in blue.
Fifth and sixth rows in green.
Seventh and eighth in purple.
And the last two rows in red. Ten rows of 3 coins turns out to be possible using only 9 coins!