Question

if -9 is added to a number and the sum is doubled, the result is 11 less than the number. Find the number

Answer 1

Suppose that x is the number we want :

- 9 added to it means :

$x + ( - 9) = x - 9$

And sum is doubled means :

$2 \times (x - 9)$

The result is 11 less than the number which means :

$2 \times (x - 9) = x - 11$

Now let's find the x ...

$2x - 18 = x - 11$

Add both sides 18

$2x - 18 + 18 = x - 11 + 18$

$2x = x + 7$

Subtract both sides x

$2x - x = x + 7 - x$

$2x - x = x - x + 7$

$x = 7$

Thus that number is 7

Answer 2

Answer: 7

let x be the number

2(-9 + x) = x - 11

-18 + 2x = x - 11

2x - x = -11 + 18

x = 7