It all depends on the fraction.
1/2=.5 because half of 1 is .5 and half can be represented as 2
3.124 * 10^-4
since your decimal is coming forward you need the exponent to be negative
question seems incomplete
there are no notations for inequalities
25 divided by 5 is 5 so she gave 5 stamps each week
64 divide by 3 would roughly be 12 weeks because otherwise it would be a renainder
12 add 5 equals 17 weeks
So it should take 17 weeks
hope this is right Please ask me if any doubts
Thank you Good Luck