Question

If 3+a=4-b and 4+b=7+a, what is 3-a?

Answer 1

The answer is 4.

Explanation:

First, you have to form simultaneous equations :

`3 + a = 4 - b`

`a + b = 1 - - - (1)`

`4 + b = 7 + a`

`a - b = - 3 - - - (2)`

Next, you have to solve it :

`(1) - (2)`

`a + b - (a - b) = 1 - ( - 3)`

`2b = 4`

`b = 2`

`sub \: \: b \: = 2 \: \: into \: \: (1)`

`a + 2 = 1`

`a = 1 - 2`

`a = - 1`

Lastly, you have to substitute a-value into the expression :

`3 - a = 3 - ( - 1) = 4`

Answer 2

Explanation:

3+a=4-b

4+b=7+a

a=1-b

4+b=7+1-b

2b=4

b=2

a=1-2= -1

3-a= 3- -1= 3+1=4

3-a=4