There are 6.02 E23 atoms per mole. I'm using E23 to mean 10 raised to the 23 power, like calculators do. If you divide this number into 4.8 E25 atoms you'll get 0.7973 E2 moles which is essentially your 8.0 E1 moles when you take into account the original 2 significant figure number. See 0.7973 times 100 = 79.73 moles. It helps a lot if you include the units with your numbers.