Question

The sum of two numbers is 61.The larger number is 4 more than two times the smaller number. What is the smaller number?

Answer 1

a + b = 61       a > b        a = 2b + 4

2b + 4 + b = 61
3b + 4 = 61
3b = 57
b = 19

Answer 2

smaller number = x
larger number = y

$\left \{ {{y+x=61} \atop y=2x+4}} \right.$

solve the system of equations by substitution:

(2x+4) + x = 61
3x+4 = 61
3x=57
x=19

Plug x into the top equation and solve for y:

y + (19) = 61
y = 42