What number is subtracted from both side of x plus 5 equals 15 when solving for x?

Answer 1

5 is subtracted from both sides of the equation. x + 5 = 15: x+5 (-5) = 15 (-5);

when you subtract 5 on the left side of the equal sign the +5 (-5) cancel each other out to equal 0; when you do something to one side of the equal sign you must do the same thing to the other side; so subtract 5 from 15, and you are left with x + 0 = 10

which is x = 10.

When solving for x, you want to end up with x all alone on one side of the equal sign. You have to subtract (or add) the total sum on the x side to both sides of the equal sign.

5 Additional Examples when solving for x:

x + 7 = 13: you have to subtract 7 from both sides of the equal sign

x + 7 (-7) = 13 (-7) so x = 6

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x + 2 + 4 = 20: you have to subtract 2 and 4 from both sides of the equal sign

x + 2 + 4 (- 2) (- 4) = 20 (-2) (-4), so x = 14

a shortcut would be to subtract 6 from both sides of the equal sign since 2+4=6

x + 2 + 4 (-6) = 20 (-6) so x = 14

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x - 3 = 18: you have to add 3 to both sides of the equal sign

x - 3 (+3) = 18 (+3) so x = 21

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x - 5 - 4 = 17: you have to add 5 and 4 to both sides of the equal sign

x - 5 - 4 (+5) (+4) = 17 (+5) (+4), so x = 26

a shortcut would be to add 9 to both sides of the equal sign since -4 - 5 = -9

x - 5 - 4 (+9) = 17 (+9) so x = 26

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x + 7 - 3 = 19: you have to subtract 7 and add 3 to both sides of the equal sign

x + 7 - 3 (-7) (+3) = 19 (-7) (+3) so x = 15

a shortcut would be to subtract 4 from both sides of the equal sign since 7 - 3 = 4

x + 7 - 3 (-4) = 19 (-4) so x = 15

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I hope this helps you understand. You do not have to use the parentheses when adding or subtracting on either side of the equal sign. I just used them to make it easier to read.