Validating multiple questions

Validating multiple questions

Hi everyone,

I have a survey which requires the respondent to allocate "points" across multiple questions using a sliding scale.


For example, allocate 50 points to allocate to across four different questions (on each page). 
Question 1.  (0 - 50)  
Question 2. (0 - 50)
Question 3. (0 - 50)
Question 4. (0 - 50)

Questiona
1. Is there any way that using logic / custom function / deluge etc etc.. that prior to the respondent moving to the next page the SUM  of the four questions equal 50.    
2. If not, what methods or advice might this group have to meet the allocation requirement?

Thanks

Andrew