Wire Length — Rectangle Perimeter Problem

A wire 80 cm long is bent into a rectangle. Two sides are 10 cm each. What's the length of one longer side? The key: wire length = perimeter. Subtract the two known sides, then halve what's left. Option E (60 cm) is the most common wrong answer — students forget to divide by 2 and give the combined length of both longer sides.

Rectangle perimeter questions where one pair of sides is given and the other must be found appear regularly in the easy band of OC MR. The 'wire = perimeter' framing is a classic presentation. Students who know perimeter = 2L + 2W and rearrange correctly always score here.

The examiner is testing whether students can set up the perimeter equation with one unknown, subtract the known sides, then halve the remaining length to find one side. Option E (60) directly catches students who subtract the short sides but forget to divide by 2. Option A (15) catches students who halve 80 first (to get 40) and then subtract 10 + 10 + 5.

A wire or string of given total length is bent into a rectangle. Two sides (the shorter ones) are given. All wire is used, so wire length = perimeter. Students must subtract the two known sides from the total, then divide by 2 to find each unknown (longer) side.