(0.312−0.03) In the subtraction of 0.312−0.03. The number 0.03 has two digits after decimal. So, 0.312−0.03=0.282 But only upto two decimal places it can be written as 0.28 . Now, ‌
0.501
0.05
the term 0.05 has two digits after decimal ‌
0.501
0.05
=10.02≈10 Now, 10.02×0.28=2.8056 But this number should be rounded of to 2.8 . So, number of significant digit is 2 .