Shaded Nets

A flat net is shown with its panels coloured in. The options are 3D solids. You pick the solid the net folds up into.

Two things have to match: the shape of the solid, and the colours on it. Shape first. It takes seconds, and it throws out pictures whose colours are all correct.

There are no boxes here. Every face of a box is a rectangle, so a box has nothing for this question to ask about.

The method

Five beats: name the solid, say which kind of net, walk the band, account for every face, check the ends.

1. Name the solid. Count the panel shapes. The shape that appears exactly twice becomes the two ends. Every other panel is a rectangle, and the rectangles wrap round the middle as one band. Three rectangles and two triangles make a tent or a ramp. Five and two pentagons make a pentagonal prism. Six and two L-shapes make a solid with a step.
2. Say which kind of net. Are all the panels of one shape the same colour? Then the ends are the odd one out, and no folding is needed. If two same-shaped panels carry different colours, you must fold. Only 4 of our 25 exam-level nets are the easy kind.
3. Walk the band. Start at the panel the ends hang off. Count along the rectangles, one at a time. This beat has a name: the band walk. Which face a panel lands on is fixed by the folding, never by which colour turns up most.
4. Account for every face. Match the ones you can see, one at a time and every one of them — stopping as soon as one matches is how the near-misses win. The ones round the back you cannot check, so count them instead. "Three grey panels on the net, two showing, so the third is round the back."
5. Check the ends. A mirror keeps every colour and swaps the two ends over. Nothing you can count will catch it. Only the fold says which end is which.

About 25 to 35 seconds each. An easy net takes 15, so bank that time for the stepped solids.

Rules to watch

• Faces that meet at an angle are still separate faces. On a stepped solid the tread and the riser are two different panels. Side by side on the net, in close colours, they read as one.
• Most of the solid is out of sight. A ramp or a tent shows two faces of five, a pentagonal prism three of seven, a stepped solid five of eight. A colour that lands out of sight is real, and it settles nothing.
• Hunt a colour used only once. It sits on exactly one face, so any picture showing it twice is out. Eleven of our 25 nets have one.
• The palest picture is not the answer. The colours are shared out evenly on purpose, so how pale a picture looks tells you nothing.

Watch for these traps

We looked at all 100 wrong solids in our 25 exam-level questions.

• One face the wrong colour. 61, and at least one on every question, usually two or three. It is the right solid with one face recoloured. So little is showing that one wrong face is easy to miss. Beat 4 answers it: check every face, not the first that matches.
• The right colours on the wrong solid. 20, on 20 of the 25 questions. Sixteen are a plain box. The colours are copied off the answer, and it shows the same number of coloured faces. So counting patches tells you nothing. Beat 1 catches it in two seconds.
• The mirror image. 19, on 19 of the 25. The same solid built back to front. Every colour is still there, so counting will never find it. On 17 of the 19 the giveaway is one face: the near end is wearing the far end's colour. On the other two, the two sloping faces have swapped.

And one trap not to go hunting for. On the four nets where every rectangle carries one colour there is no mirror at all. Those solids and their mirrors are the same picture, so a mirror there would be a second right answer. All 19 sit on nets that colour two same-shaped panels differently. Beat 2 tells you which kind you are in.

Stuck? Work down this list rather than guessing.

1. Name the solid from the panel shapes. Cross out every picture built on another one.
2. Find a colour used once on the net. Any picture showing it twice is out.
3. Compare the two biggest faces, let the small ones go, then pick and move on.

Try these yourself

Now have a go yourself — tap the solid that the net makes.

Related

• The complete 11+ question-type guide
• Cubes and Nets — the same folding, with symbols on a cube
• Building Blocks — which set of blocks builds the shape

All example questions come from the Brainblox question bank — practise this question type inside 15 arcade games, timed mock exams and focused practice. Brainblox is an independent app: not affiliated with, endorsed by or licensed by any exam board, school or assessment publisher, and it contains no past papers.