subtracting negatives

[weissicycle]

subtracting negatives,why is -12-64= -75, my 10 yr old asked why isn't it -12-(+64)=59

He thinks (and rightfully so) that if the # doesn't have a sign in front of it, it is +, so the problem -12-64=?, is really -12- (+64), which really does =+59

 

[Deleted member 4993]

subtracting negatives,why is -12-64= -75, my 10 yr old asked why isn't it -12-(+64)=59

He thinks (and rightfully so) that if the # doesn't have a sign in front of it, it is +, so the problem -12-64=?, is really -12- (+64), which really does =+59

Not really - but I hope you meant 52.

Thought is correct but process is wrong!

It is best explained - to you - by using "credit" money.

Suppose you already have a negetive balance of $12 in your credit card.

Now you went out and took more money from it through cash advance (64 positive dollars).

Without considering the horrendous charges that may accrue - how much is your debt to the credit card now?

 

[mmm4444bot]

Has your 10-year-old been taught anything yet about the Real number line?

Subtracting 64 means moving sixty-four units to the left.

Hence, if you start at -12 on the number line, and you then move to the left, there is no way to arrive at a positive result because you're moving away from zero.

Draw a picture, if needed.

Require more clarification? Please feel free to say so.

Cheers ~ Mark :cool: