Bunuel wrote:
A one meter long wire is to be marked for cutting at intervals of fifths and thirds. How long, in meters, is the largest segment of the wire if the wire is cut at the marked intervals?
A. 1/15
B. 2/15
C. 1/5
D. 4/15
E. 9/15
So when we mark at intervals of thirds, the marks are at the positions 1/3 and 2/3 from the starting point.
And when we mark at intervals of fifths, the marks are at the positions 1/5, 2/5, 3/5, 4/5 from the starting point.
To make the comparison easier, we can write 1/3 and 2/3 as 5/15 and 10/15 respectively.
Similarly, we can write 1/5, 2/5, 3/5, 4/5 as 3/15, 6/15, 9/15 and 12/15 respectively.
So, now if we look at all the above 6 marks one by one from the starting point, the marks are at the following positions:
3/15 from start, 5/15 from start, 6/15, 9/15, 10/15 and 12/15 respectively. Cutting at exactly these 6 marks, we will get 7 pieces of wire which will be of following lengths (from the start):
3/15, 2/15, 1/15, 3/15, 1/15, 2/15 and 3/15 respectively. The largest length as we can see is that of 3/15 or 1/5. Hence
C answer