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Question:

southern30
southern30
Student

solve the following:  -2 + 5 = what?

is the answer a.13  b.+3  c. -7  d. +7

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Posted by southern30 on Tuesday August 11, 2009 at 7:10 PM and tagged with math.

Answers:

  1. rleahennis
    rleahennis Teacher
    High School - 10th Grade

    eNotes Editor

    To answer this question, and others like it, re-write the equation and reverse the +s and -s:

    In this instance, your equation can be re-written as 5 + -2 , which is the same as 5 - +2 (change the plus sign to a minus and the negative symbol to positive) or

    5-2, which I bet you can answer!

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    Posted by rleahennis on Tuesday August 11, 2009 at 7:18 PM

  2. cburr
    cburr Teacher
    Middle School

    eNotes Editor

    Another way to approach this is to picture a number line.  In the middle is 0.  Stretching out to the right is what we are used to, 1,2,3,4,5 etc.  Stretching out to the left is the negative numbers, -1, -2, -3, -4, -5, etc.

     

    If you start at -2 on the number line, and add 5 -- that is, move 5 to the right, you end up at +3.

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    Posted by cburr on Tuesday August 11, 2009 at 7:57 PM

  3. sumedha
    sumedha Student

    -2+5=+3

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    Posted by sumedha on Tuesday August 11, 2009 at 10:31 PM

  4. neela
    neela Teacher
    Graduate School

    eNotes Editor

    Experts have given their considered solutions. Please see whether my solution is of any use to you which is particularly based on group theory we study here in mathematics of around 6th to 9th grade :

    To solve -2+5

    -2+5= -2+(2+3) , as 5=2+3

    -2+(2+3)=(-2+2)+3, by associative law.

    =0+3

    =3, as 0 is the additive identity, i.e. 0+x=x+0=x, x being any number.

    Second method.

    -2+5= 5+(-2) , by commutative law, i.e., a+b=b+a for any two numbers a and b are commutative under addition.

    5+(-2)= 5-2, as +(-a) or -(+a)=-a, by rule of sign.

    5-2= (3+2)-2

    (3+2)-2= 3+(2-2), by associative law.

    3+(2-2)=3. As 2 and -2 are mutually additive inverse of each other.

    Thanks for giving an oppotunity to express.

    Hope this helps.

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    Posted by neela on Tuesday August 11, 2009 at 10:37 PM


  5. surajverma8 Student
    Doctorate

    As I have learned in indian explanation, I want to convey you that:

    1. if we add two alzebraic digits then we apply the sign which digit is greater between them. Same way:

    "-2+5"

    we know that '5' is greater than that of two so we shall apply the '+' sign and because there are two opposite signs so "2" will be deducted from '5' and then:

    answer will be "+3".

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    Posted by surajverma8 on Wednesday August 12, 2009 at 12:19 AM

  6. bhacho
    bhacho Student
    Graduate School

     

    +3

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    Posted by bhacho on Wednesday August 12, 2009 at 6:07 AM

  7. coolnity
    coolnity Student
    High School - 10th Grade

    3

     

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    Posted by coolnity on Saturday August 15, 2009 at 1:02 AM

  8. sdiva1982
    sdiva1982 Teacher
    Elementary / Primary

    Integer Rules:

    1. Same sign = add and take the sign

    Positive + Positive = add and answer is positive

    Negative + Negative= add and answer is negative

    2. Different Sign = subtract and take the sign of the larger number.

     

    -2+5

    Different signs Rule 2 = subtract and take sign of larger number (5)

    -2-5 = + 3

     

    Sources:
    http://www.chester-nj.org/~mccarthy/INTEGER%20RULES.htm

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    Posted by sdiva1982 on Wednesday August 19, 2009 at 4:17 PM


  9. suvetha Student
    High School - 9th Grade

    The answer is 3

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    Posted by suvetha on Saturday August 22, 2009 at 4:53 AM


  10. jynx1955 Teacher
    Middle School

    My students hear this from me:

    ADDING and SUBTRACTING "LIKE" SIGNS - Add & Keep Sign.

    ADDING "UNLIKE" SIGNS - Subtract the absolute values of both integers and keep the sign of the largest absolute value.

    SUBTRACTING "UNLIKE" SIGNS - Turn the problem into an addition problem by reversing the sign of the second integer:

        -3 minus +4     is the same as    -3 plus -4     or -7

        +3  minus -4    is the same as   +3 plus +4    or +7

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    Posted by jynx1955 on Sunday October 4, 2009 at 4:25 PM