HEADS AND TAILS
Linda arranged 16 coins in a square, alternately placed showing heads and tails, as in the figure below. ‘All you have to do is to rearrange the coins so that the rows are all heads in the first row, all tails in the next, all heads in the third and all tails in the last row.’
‘What’s the catch?’ asked David.
‘Oh yes,’ said Linda, ‘I almost forgot! You have to do it by touching only two of the coins.’
David pondered for a moment. ‘Is it a trick?’
‘Hmm, not really. Think about my rules.’
What is the neatest solution?