In our number system the base is ten. If the base were changed to four you would count as follows: 1,2,3,10,11,12,13,20,21,22,23,30,… The twentieth number would be:
<spanclass=′latex−bold′>(A)</span> 20<spanclass=′latex−bold′>(B)</span> 38<spanclass=′latex−bold′>(C)</span> 44<spanclass=′latex−bold′>(D)</span> 104<spanclass=′latex−bold′>(E)</span> 110 modular arithmeticnumber theory