Everyone who sent in answers had to think about how to show the order of each little calculation. Some wrote down the answer after each step, some used the 'rule' that any multiplying and dividing should be done before the adding and subtracting, and some put brackets around bits that had to be done first.


All of the calculations shown below lead to $100$ - but you could think about whether they have chosen the best way to write their answers.



Rayner from Tao Nan School, Singapore sent in these two:


$$1 \times2 \times3 + 4 + 5 + 6 + 7 + 8 \times9 = 100$$
$$123 + 45 - 67 + 8 - 9 = 100$$

Christopher from Tattingstone School:

First of all I put down the numbers 1 to 9 on a bit of paper and kept adding, multiplying, dividing and subtracting until I got the right answer and these are what I came up with.
$$9 \times8 + 7 + 6 + 5 + 4 + 3 + 2 + 1 = 100$$
$$7 \times9 \times2 - 6 -5 - 4 - 3 - 8 \times1 = 100$$

Rowena:

$$1 + 2 + 3 + 4 +5 \times6 - 7 + 8 + 9 =100$$

I just tried some sums until I found one that worked.

Helena from Tattingstone School:

$$7 \times8 \div4 \times6 + 1 + 3 + 5 + 9 - 2 = 100$$



Sally from Tattingstone School:


$$1 \times2 + 3 \times4 \times5 - 6 + 7 + 8 - 9 = 100$$


Gina and Kate from Yarm Primary School, Stockton-on-Tees:

\begin{eqnarray}9 \times 5 = &45&&&&&&&\\ &+ 8 =& 53 \\ && \times 2 =& 106\\ &&&-6 =& 100 \\ &&&&-7 =& 93\\ &&&&&+3 =& 96\\ &&&&&&+ 4 =& 100 \\ &&&&&&& \times 1 = 100\\ \end{eqnarray}

James from Yarm Primary School, Stockton-on-Tees:

\begin{eqnarray} 9 \times8 =& 72&&&&&&& \\ &+ 7 =& 79&&&&&&\\ &&+6 =& 85&&&&&\\ &&&+5 =& 90&&&&\\ &&&&+ 4 =& 94&&&\\ &&&&&+ 3 =& 97&&\\ &&&&&&+ 2 =& 99&\\ &&&&&&&+ 1 =& 100.\\ \end{eqnarray}

Jessica from Tattingstone School, UK:

I played around with the numbers ... until I had 500 which I could divide by 5.

\begin{eqnarray} 9 \times8 \times7 = &504 &&&&&\\ & + 3 = &507&&&&\\ &&& + 4 = &511&&&\\ &&&& +1 = &512&&\\ &&&&&- 6 \times2 =& 500&\\ &&&&&& \div 5 = 100 \\ \end{eqnarray}

Jason from Priory School, UK:

$$(1 \times2) + (3 \times4) \times5 + (6 + 7 + 8 + 9) = 100$$

Alexander from Crofton Junior School, Kent:


$$[(1 + 2) \div3] + 4 + (5 \times6) + (7 \times8) + 9 = 100$$

\begin{eqnarray} 9 \times 8 =& 72 \\ &+ 1 + 2 + 3 + 4 + 5 + 6 + 7 = 100\\ \end{eqnarray}

Daniel from Anglo-Chinese School, Singapore:

\begin{eqnarray}
(1 + 2 + 3 + 4) \times(((-5 + 6) \times(-7 + 8)) + 9) &=& 10 \times(((-5 + 6) \times(-7 + 8)) + 9)\\&=& 10 \times((1 \times(-7 + 8)) + 9) \\&=& 10 \times((1 \times1) + 9) \\&=& 10 \times(1 \times9) \\&=& 10 \times10 \\&=& 100 \end{eqnarray}

Lennox from Norbury Manor Primary School:


$$(9\times 8) + (4 \times 6) + 9 + 1 + 5 + 2 + 3 = 56 + 24 + 20 = 100$$

Declan and Harry from Norbury Manor Primary School:


$$(7 \times8) + (4 \times6) + 9 + 1 + 5 + 2 + 3 = 56 + 24 + 20 = 100$$