7-y=-2 is the answer 9 or 5

Question

I dont know which 1 is right my brother says 9 but i say 5 but i just started learing this in class and i need help

Answer 1

One way is to add y to both sides to get 7=y-2 and then add 2 to both sides giving 7+2=y so y=9.

Also, a good rule to remember when working with subtraction:

If a smaller number is subtracted from a larger one, the difference will be positive.

If a larger number is subtracted from a smaller one, the difference will be negative.

Since the difference is negative, we know that y>7, so of the two choices, 5 or 9, only 9 makes sense.

Answer 2

Hi April, 

there are 2 ways to approach this problem (depending on what you have learned so far)

1. You can plug in answers:

7-9=-2 or 7-5=2, you decide 

2. You can solve for y ( this means you always want the variable y by itself one one side)

7-y=-2

i.Subtract 7 from the left and right side of equal sign

7-y-7=-2-7

-y = -9

ii. Multiply or divide both sides by -1 (your goal is to get positive y by itself)

-y * (-1) = -9 * (-1) [rule: multiply 2 negatives to get a positive]

y = 9

check your answer: 7-9=-2 

Answer 3

to put it simply, the answer is 9, as the others indicated.  The great thing about math is you can always double check your answer by putting the number in the equation to see if it makes sense.  7-5=2, so just by logical reasoning you can see that 7-9=-2, and the answer makes sense!

Just a tip for anybody, you can always plug the answer in where the letter is and see if it adds up!

Hope that helps!

Answer 4

April...simpliest way is to substitute the proposed answers... 9 or 5 into the original equation and do the operation. You will see which one is correct...then you will be the MASTER