Question 518202
The three digits: a, b, c, d
:
"The sum of the digits is 12."
a + b + c + d = 12
:
"The digit in the thousandths place is 3 times the digit in the tens place."
a = 3c
"The digit in the tenths place is one more than the digit in the hundredths place."
c = b + 1
or
b = (c-1) 
:
a + b + c + d = 12
Replace a and b
3c + (c-1) + c + d = 12
5c + d = 12 + 1
5c + d = 13
Assume that c has to equal 2, therefore
5(2) + d = 13
10 + d = 13
d = 13 - 10
d = 3
find the rest of the digits
a = 3(2) = 6
b = 2-1 = 1
c = 2
d = 3
then
6123 is the number
:
Assume that c has to equal 1, therefore
5(1) + d = 13
5 + d = 13
d = 13 - 5
d = 8
find the rest of the digits
a = 3(1) = 3
b = 1-1 = 0
c = 1
d = 8
then
3018 is the number
:
"To the nearest ten, the number rounds to 30." Not sure what bearing this has on this problem.