In Single-Product CVP analysis, we have one product that the company is making so we need to work out our calculations based on an individual basis.
But in Multi-Product CVP analysis, we have more than one product that the company is making so we need to work out our calculations based on Weighted Average basis which means we have to do our calculation on a Total basis (i.e. taking total contribution and total sales revenue to get C/S ratio and as such)
Yes it is true (assuming that the products continue to be produced in the same ratio).
Have you not watched my free lectures on this? The lectures are a complete free course for Paper PM and cover everything needed to be able to pass the exam well.