Did you solve it? The simple question almost everyone gets wrong

Earlier today I set you these six stencil puzzles, based on a IQ test for children devised by the American psychologist Grace Arthur in the 1920s.

In each puzzle there is a patterned square at the top. The challenge is to work out how to create this square by placing some of the available stencils and coloured blocks on top of each other.

Here’s the first example. It is very simple, but about 90 per cent of people get it wrong whatever their IQ.

Solution: KBD

Did you fall into the trap? (I did when I looked at the puzzle first.) Most people say KED because they haven’t checked the size of the cross carefully enough.

Here are the other five questions. Some have more than one correct answer.

Solution: BCFD/BFCD

Solution: GICJDK

Solution: HFIBEL

Solution: JILBFKD, JLIBFKD, JILBKFD, JLIBKFD

Solution: KJEGCA

The images today come from the app Stenciletto, which reimagines Grace Arthur’s stencil test as a bit of fun.

It was developed by Jane Braybrook for her disabled son to help him with his learning. To read more about the app and Braybrook’s story, read my original post here.

Stenciletto is available for iPhones on the AppStore, and for Android devices at Google Play. More information can be found here.

I set a puzzle here every two weeks on a Monday. I’m always on the look-out for great puzzles. If you would like to suggest one, email me.

I give school talks about maths and puzzles (online and in person). If your school is interested please get in touch.

NEWS FOR UK READERS: On Saturday 8 July, the print edition of the Guardian in the UK will include a Summer puzzle supplement that – certainly for readers of this column – will provide hours of entertainment. It includes some wonderful pencil-and-paper logic puzzles created by one of the UK’s top setters, as well as a variety of crosswords including a themed Jumbo by Brendan and the first ever appearance in the UK of a ‘Marching Bands’ puzzle. Make a note in your diary to buy the paper on 8 July!