Lisa and Alana (Age 10, Sudbourne School, Lambeth) used words to explain how they worked out the next number:

"The answer to what is the next number is.163 because the difference between 3 and 7 is 4 and the next difference (between 7 and 19) is 12 which is 3x4 the difference after that (between 19 and 55) is 36 which is 12 (the last difference and 3 (the first number, also the number timsed by 4 to get 12.) So we just added 108 to 55 which equals 163".

Sinan Ersanli (Age 11, IRMAK Primary School, Istanbul, Turkey) says much the same thing with numbers:

Sarah H (Age 12, Annesley College, Adelaide South Australia) explained it a slightly different way: "I figured it out by working out how much the difference is between the four numbers. Then I found that all the numbers between are all factors of three. So, I times each of the between numbers by three. When I got to 55 times three I got 108. Then I added 55 and 108 and I got 163. This was the answer I got."

Shivana Thirumoorthy (Age 10, Henry Park Primary School, Singapore) has another way of writing it: The answer is 163. n x 3 - 2 n being the previous number

Example 19x3-2=55

Emir Asari (Age 11, IRMAK Primary School, Istanbul, Turkey) worked it out in a similar way.

The following people also explained their thinking quite well: Laura Plant (Age 10, St Ives School, Haslemere).

Ruyi Yuan (Age 12, Annesley College, Adelaide South Australia)

Alex Gibson (The Abbey, Woodbridge, Suffolk)

Jason Day (Priory School)

Ruth Howlett (Age 9) and Jessica Chapman (Aged 10, St Lawrence Primary School, Lechlade).

Jenny Sharratt (Age 10) Emily Carlyle, Caroline Foster, Natalie Poon & Rebecca Sherwood (Age 11/12, The Mount School York)

Kathryn, Katerina and Nicola (Age 10) and Andrew (Age 9) Primary Maths Club, International School of Toulouse.

Leyla Aksu, Gizem Girav, Ünal Öz, Melis Onalan, Hüma Üster, Ece Demir, Idil Ata&cced;, Gizem Koçkesen, Altay Alpagut, Ece Köprülü, Simin Araz, Eda Sezginer, Ece Oney, Cana Arican, Sinan Ersanli, Melike Altinta, Efsane Karayilanoglu, Emre Ilker, Ilayda Özyurt, Baran Karakuzu (Age 11/12, IRMAK Primary School, Istanbul, Turkey).

Thomas Harley (Age 9) and Justin Thurbold (Age 10), Tatingstone School)

Michael Molinari (Age 10/11, St Francis Catholic Primary, Essex)

Christina Ivanova (Malborough Primary)

And finally, a short neat explanation from Steven Cummins (Age 8, Burpham Primary School, Guildford, Surrey)

"I looked at the sequence of numbers and worked out the differences between each one. These were 4, 12, 36. I realised that 3 x 4 = 12, and that 3 x 12 = 36, so the next gap would be 3 x 36. That is 108, so the next number is 163."