Consecutive numbers

a+b+c+d=90
b=a+1
c=b+1
d=c+1

a+b+c+d = 90
a-b = -1
b-c = -1
c-d = -1

Row 2 - Row 1 → Row 2
a+b+c+d = 90
-2b-c-d = -91
b-c = -1
c-d = -1

Row 3 - 1/-2 · Row 2 → Row 3
a+b+c+d = 90
-2b-c-d = -91
-1.5c-0.5d = -46.5
c-d = -1

Row 4 - 1/-1.5 · Row 3 → Row 4
a+b+c+d = 90
-2b-c-d = -91
-1.5c-0.5d = -46.5
-1.3333d = -32


d = -32/-1.33333333 = 24
c = -46.5+0.5d/-1.5 = -46.5+0.5 · 24/-1.5 = 23
b = -91+c+d/-2 = -91+23+24/-2 = 22
a = 90-b-c-d = 90-22-23-24 = 21

a = 21
b = 22
c = 23
d = 24

Our linear equations calculator calculates it.