when James crossed the finish line of a 60 metre race, he was ahead of Robert by 10 metres and ahead of Sam by 20 metres. Suppose Robert and

I will assume the boys have all run at a constans speed right rom the beginning of the race.

When Robert has run 50, Sam has run 40 metres 

so Sam has has run 4/5 as far as Robert.

If this ratio stays the same then when Robert has run 60m Sam will have run  4/5 of 60 = 48 metres.

So I think that Sam will be 12m behind when Robert crosses the finish line.  :)

it is 10 metres

Well...if James beat Robert by 10 m and Sam by 20m, then Robert will beat Sam by 10m

Yeah, Melody....I hadn't comsidered that.....it seems logical....!!!

Thanks Chris,

Of course the boys wouold not run at exactly the same speed the whole way but if they did then what I have done makes some sense to me.