Sum blocks based on value

[glynn1969]

Hello

I have a simple excel book where Column a contains numbers 1 and 2, the 2 represents the start of a block of 1s, I want a formula that will look for a number 2 in column A then sums up all the entries of column b that have a value of 1 in column A until a 2 is found again in column A then repeat the sum process.

Any help much appreciated.

 

[glynn1969]

@glynn1969 in future please do not mark a post as the solution when it does not contain one. Especially as you are still looking for help.
Thanks

Sorry didn't realise I had