The sum of three numbers is 4. The second number is 1 more than twice the first. The sum of the first and third is –1. Find the numbers.

1st condition: x + y + z = 4
2nd condition: y = 2x + 1
3rd condition: x + z = - 1 <=> z = - x - 1

Based on the 2nd and 3rd, we replace the 1st as following:

x + 2x + 1 - x - 1 = 4 <=>

2x = 4 <=>

x = 2

Since x = 2, we solve the 2nd as following:

y = 2x + 1 <=>

y = 2*2 + 1 <=>

y = 4 + 1 <=>

y = 5

Same thing for the 3rd:

z = - x - 1 <=>

z = - 2 - 1 <=>

z = - 3