In an office of 1200 employees, the ratio of urban to rural members of staff is 8 : 7. Afier joining of some new employees. out of which 20 are rural, the ratio becomes 5 : 4. The number of new urban employees is:

Let say,number of new employee joined is$$=x $$.

so, newly joined rural employees are 20(given) then,number of newly joined urban employees$$=(x-20).$$

previously,

number of urban employees$$=1200×8/15=640.$$

so, number of rural employees

$$=1200-640=560.$$

after joining of new employees the new ratio become $$=5:4.$$

$$((x-20)+640):(20+560)=5:4$$

or,$$4x-80+2560=2900$$

or,$$4x=2900-2480=420.$$

or,$$x=105.$$

so,number of new urban employees

$$=105-20=85.$$

B is correct choice.