Answer:
a) true.
if 3 can divide a without remainder, then a = 3×x.
doubling that number makes it 2×3×x. because of that still included factor 3, it is still divisible by 3 without remainder.
b) false.
example :
a=6, b=4, c=3
bc = 12
6 can divide 12 without remainder, but 6 cannot do that with 4 and not with 3.
or
a=7, b=35, c=10
bc=350
7 can divide 350 without remainder, and can do that also with 35, but not with 10.
