Two attendants earn $6240 and $6220 per annum, respectively, exclusive of a bonus of $2640 per annum.

if both have a pension deduction of 20%, the difference in the pension deduction of the two attendants on a semimonthly basis is ... ?

The difference in annual earnings is $6240 - 6220 = $20. 20% of that is $4. There are 24 semi-months in a year, so the difference in amount deducted is about

... $4/24 = $ (1/6) ≈ $0.17

If the payroll department is paying attention, the difference in deducted amounts will be $0.16 2/3 over the year. Some paychecks, it will be $0.16, and others it will be $0.17.