KA-0136Ordering and ranking from clues
5 points, difficulty 3 of 3Level 3–4about 105sFour children stand in a line. Ana is not first. Bo stands directly behind Ana. Cal is last. Who is first?
Hints
Take them one at a time. The first gives nothing away.
1A nudge
Try Ana in each allowed position.
2The strategy
Cal is fixed at position four. Ana cannot be first, so try Ana second and Ana third in turn, remembering that Bo must be immediately behind her.
3The full solution
If Ana were third, Bo would be fourth - but Cal is fourth. So Ana is second, Bo third, and Dee is left for first.
Solution— no shortcut on this one
Cal takes position 4. Ana is not first, so she is second or third. If Ana were third, Bo would have to be fourth, which Cal already occupies - impossible. So Ana is second and Bo is third, leaving Dee at the front. The line is Dee, Ana, Bo, Cal. The transferable idea: when one clue leaves only two possibilities, test both - a contradiction in one of them settles the whole arrangement.
Why this is on the test: Directly behind is a much stronger clue than behind, and using it to eliminate rather than to place is what cracks the question.