In general, unless otherwise specified, you should assume the range to be inclusive of the beginning and ending numbers, 10 & 20 in this example.
Since neither of these numbers are multiples (even integer multiples that is) of 10 or 20, they won’t show up as multiples of interest. Should either the beginning or ending range numbers be numbers satisfying the condition, then they would be included in the list. For example, if you want multiples of 6 between 12 and 20, then 12 would be part of the desired list (along with 18).
Hope this helps!
30
It is: 30
It is: 6.78*10^6 = 6,780,000
Multiple of 10 between 599897 and 600011
60
To be a multiple of 4, 10 and 20 the number must be a multiple of their lowest common multiple. lcm(4, 10, 20) = 20 What is required is a multiple of 20 between 61 and 107. The numbers 80 and 100 both satisfy the problem of being between 61 and 107 and being a multiple of 4, 10 and 20.
Two multiple of 10 lie between 392 and 418. They are 40 and 41.
13 has a multiple of 26
9990
It is: 6250
16
The only such number between 55 and 101 is 80.