Answer: The numbers are:
965
875
785
695
Explanation:
We have a 3 digit number that can be written as:
a*100 + b*10 + c
Where a, b, and c are single-digit numbers.
a is the hundreds
b is the tens
c is the unit.
We know that:
"The sum of the tens digit and the hundreds digit of a number is three times the units digit."
a + b = 3*c
" 1/5 of the sum of all three digits is 1 less than the units digit."
(a + b + c)/5 = c - 1
Then we have the two conditions:
a + b = 3*c
(a + b + c)/5 = c - 1
From the first one, we can write:
(a + b)/3 = c
Replacing that in the other equation we get:
(a + b + a/3 + b/3)/5 = a/3 + b/3 - 1
(4/3)*(a + b)/5 = (a/3 + b/3) - 1
(4/15)*(a + b) = (a + b)/3 - 1
(4/15)*(a + b) - (a + b)/3 = - 1
-(1/15)*(a + b) = -1
a = 15 - b
Then we can give different values for b, and find the values of a and c, where a and c must be positive.
b = 9
a = 15 - 9 = 6
Then:
c = (9 + 6)/3 = 5
(notice that a + b = 15, then c will be always equal to 5, reggardless of the values of b and a).
This number will be:
695.
if b = 8, then:
a = 15 - 8 = 7
and c = 5, same as before.
the number is 785.
If b = 7, then:
a = 15 - 7 = 8
The number is 875
if b = 6, then:
a = 15 - 6 = 9
The number is:
965