Calculate the % of calcium in 55% pure sample of calcium carbonate

Molecular weight of calcium carbonate = (40 + 12 +3 × 16) = 100g

Now, pure calcium carbonate (100 %) weighs 100g

It implies that 55 % pure sample weighs 55 g.

Now, you can proceed with the rest of the calculation as follows:

100 g Calcium carbonate contains 40 g of calcium

55 g Calcium carbonate contains (40/ 100) × 55 = 22 g of calcium

So, the percentage of calcium in the sample = 22 %

Regards