This is a good one. You have to find out what the words give you.
The sum of the three is 84 tells you
a + b + c = 84
The second number is twice the first tells you
b = 2a
and the third is 4 more than the second tells you
c = 2a + 4
------
a + b + c = 84
b = 2a
c = 2a + 4
Now make the first equation only have the letter a in it.
A + (2a) + (2a +4) = 84
a + 2a + 2a + 4 = 84
5a + 4 = 84
5a + 4 - 4 = 84 - 4
5a = 80
5a/5 = 80/5
a = 16
Use this into the other two.
B = 2a = 2(16) = 32
c = 2a + 4 = 2(16) + 4 = 36
Check your answers
a + b + c = 84
16 + 32 + 36 = 84
84 = 84
The sum of the three is 84 tells you
a + b + c = 84
The second number is twice the first tells you
b = 2a
and the third is 4 more than the second tells you
c = 2a + 4
------
a + b + c = 84
b = 2a
c = 2a + 4
Now make the first equation only have the letter a in it.
A + (2a) + (2a +4) = 84
a + 2a + 2a + 4 = 84
5a + 4 = 84
5a + 4 - 4 = 84 - 4
5a = 80
5a/5 = 80/5
a = 16
Use this into the other two.
B = 2a = 2(16) = 32
c = 2a + 4 = 2(16) + 4 = 36
Check your answers
a + b + c = 84
16 + 32 + 36 = 84
84 = 84
