There are 2 vernier calipers both of which have 1 cm divided into 10 equal division in the ain scale...

Question

The answer is given as option 3.
Please explain the solution.
 

This is the way I tried:

For C₁:
1MSD=0.1cm, 1VSD=0.09cm, LC=0.1-0.09=0.01cm.
=2.8+0.01(8)=2.88cm.

For C₂:
1MSD=0.1cm, 1VSD=0.11cm, LC=0.1-0.11=-0.01cm.
Reading=MSR+LC(VSMD)=2.8+0.01(7)=2.87cm.

Please tell where am I wrong

Answer 1

Reading 
= main scale reading upto coinciding main scale division − n × VSD 

= 3.5−7×0.09 = 3.5 – 0.63 = 2.87 cm 

For second vernier caliper, 10 VSD = 11 MSD 

 VSD =11/10​ MSD = 1.1×0.1 = 0.11 cm 
Reading =3.6−7×0.11  = 3.6 – 0.77 = 2.83 cm

Comments

Until now, I have read that the formula for Final Reading  of a vernier caliper is 'Main Scale Reading+(Least Count)(Vernier Scale Matching Division)'. I've never heard about this formula 'Reading  = main scale reading upto coinciding main scale division − n × VSD'. Could you pease explain this formula.