Building Blocks

A 3D shape sits at the top, solid all the way through with nothing hollow inside. Each option is a set of loose blocks, drawn apart. You pick the set that fits together to build it. Nothing left over, no gaps.

Start by giving up on counting. The shape and the blocks are drawn as solid pieces, with no lines marking the cubes inside. You judge size by eye. The shape also hides cubes you cannot see, which is why the question says it is solid all the way through.

The method

Five beats: read the shape and name the hard bit, run the too-long check, glance at the amount, place the biggest block, fill the last gap.

1. Read the shape and name the hard bit. Say three things about it. How long is its longest straight run? How many corners does it bend at? Is any single cube sticking out on its own? Then say what each of those forces. A bend needs a bent block, or two blocks meeting. A lone sticking-out cube needs a small block, or the end of a longer one. This replaces counting, and it is quicker.
2. Run the too-long check. Look down each set for a block longer than the longest straight run of the shape. Any set holding one is out. It cannot fit anywhere, however you turn it.
3. Glance at the amount. One second. A set holding plainly too much or too little block is out. Then stop — on some questions every set holds about the right amount.
4. Place the biggest block. In your head, in a corner of the shape. A corner pins a block down far more than the middle does, and big pieces have the fewest homes.
5. Fill the last gap. Check that what is left over really can be filled. This is where nearly every wrong set falls down.

Beat 2 is the one worth a name: the too-long check. It is the only free certain cut here, and it can never throw out the right set.

Give each question 30 to 40 seconds.

Rules to watch

• Nothing is hollow. Every cube inside the shape has to come from somewhere. There is no "we cannot see that bit".
• Blocks can be turned any way at all. A block drawn lying flat may be the one that stands upright. Judge it by its shape, not by how it is drawn.
• Do not fear a mirrored block. Tip a flat bent block over and you get the same block back. None of the 72 wrong sets in our exam-level bank is a mirrored block, so reject a set for that and you will lose the right answer.
• Bent blocks often pair up. Two of them often lock together into a neat brick, which is what happens in the example above.
• Do not pick the set whose biggest block is smallest. Sets often fail for holding something too big, so smaller feels safer. It is not. Use the too-long check instead.
• Start with the hardest block. A plain straight brick fits almost anywhere and tells you nothing. A bent block tells you nearly everything.

Watch for these traps

We looked at every wrong set in our eighteen exam-level questions.

• The set that nearly fits. 57 of the 72 — close to four in five. The right amount of block, sensible pieces, and still they will not fill the shape: you end up with a gap you cannot fill and a block you cannot place. Only beats 2 and 5 find these. On two of our questions every wrong set is one, so size crosses out nothing.
• One block too many, or one too few. 9 of the 72. It is one whole block, never one cube, so the gap runs to two, three or four cubes — big enough to see. On one of ours the wrong set is the right two blocks with a third piled on.
• A block of the wrong size. 6 of the 72. One piece is the wrong size, and with no lines drawn inside it that is hard to see. Compare the block against a part of the shape, not against the other blocks.

Stuck at 35 seconds? Cross out the too-long sets and the wrong amount, then pick from what is left. This type gives more free cuts than most.

Try these yourself

Now have a go yourself — tap the set that builds the shape.

Related

• The complete 11+ question-type guide
• Complete the Shape — find the piece that fills the gap
• 3D Rotation — the same shape turned, and the mirror trap

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.