Ihave between 30 and 50 pennies. when i put them in piles of 5 there is still one left over. when put them in piles of 4s, i have one penny left over. how many pennies do i have?

If you put them in piles of 5, then it could be:

30
35
40
45
50

but you have one left, so it could be then

31
36
41
46
51

if you put them in piles of 4 then it would be:

32
36
40
44
48

and if one is left then

33
37
41
45
49

and the only number both of those with one left in the ppile is 41!!