Answer:
The least number of coins that could have been stolen is 3,930.
Step-by-step explanation:
In the beginning, there are N coins to be distributed among 17 pirates, and we know that if we divide evenly these coins, there are 3 coins remaining.
Then we can write the total number of coins as a multiple of 17 plus 3.
N = 17*k + 3
where k is an integer.
After that, a pirate is killed, so now we have 16 pirates, and now there are 10 coins left, so now we can write N as a multiple of 16 plus 10:
N = 16*j + 10
where j is an integer.
Finally, having 15 pirates, the total number of coins can be divided evenly, then N is a multiple of 15
N = 15*m
where m is an integer.
So we have these 3 equations:
N = 17*k + 3
N = 16*j + 10
N = 15*m
So we can express equations like:
15*m = 16*j + 10
15*m = 17*k + 3
Where we need to find solutions such that both of these variables are integers.
For the first one we can write:
15*m - 16*j = 10
One way to do it, is to write this like a linear equation:
m = (16*j + 10)/15
Graph this, and find the pairs of points in the line that have bot integer values, or we can just find some values of j such that:
16*j + 10 is a multiple of 15.
For example, with j = 5 we have:
m = (16*5 + 10)/15 = 6
so j = 5 and m = 6 is a possible solution.
Now if we use m = 6 in the other equation:
15*m = 17*k + 3
we can see if k is also an integer:
k = (15*m - 3)/17
replacing m by 6:
k = (15*6 - 3)/17 = 5.1
This solution does not work.
Let's find others:
if j = 20 (at this point we already know that the possible values of j "jump" by 15 units, like 5 + 15 = 20) then:
m = (16*20 + 10)/15 = 22
Then:
j = 20 and m = 22 is another solution.
Same as before, let's use m = 22 in the equation for k:
k = (15*22 - 3)/17 = 19.2
Let's find another solution for m.
if j = 35
m = (16*35 + 10)/15 = 38
Using this value of m in the k equation we get:
k = (15*35 - 3)/17 = 33.4
Let's find another solution for m.
if we take j = 50 we get:
m = (15*50 + 10)/15 = 54
Using this in the k equation we get:
k = (15*54 - 3)/17 = 47.5
Eventually, for j = 5 + 15*16 = 245 we get: (arrived by iteration, just try each time using the previous value of j plus 15)
m = (16*245 + 10)/15 = 262
replacing this in the k equation we can find:
k = (15*262 - 3)/17 = 231.
So the first solution is:
j = 245, m = 262, k = 231
Then:
N = 262*15 = 3,930
The least number of coins that could have been stolen is 3,930.
