TenMarks teaches you how to multiply integers using order of operations.
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How to Multiply Integers using Order of Operations Now let’s learn about multiplication when it comes to order of operations. We’re given two problems. The first one has two parts. First part says, (-2)*5*(-9). Since the there are three numbers being multiplied, the rule is we multiply them two-by-two. So let’s do the left to right, (-2)*5, (-2)*5=-10. Again, key to remember, when two digits have being multiplied, of the sign are different, the end result has a negative sign. This one has a sign of negative, two has a sign of negative and five has a sign of positive. So the multiplication will be a negative sign. 2*5=10, negative and positive makes a negative. So now that I have (-2)*5=-10, the next thing we’ve got to do is multiply the third digit, which is (-10) is what came out of this, times (-9). (-10)*(-9) =90, and since both signs are negative, the value is positive. So the answer here is 90. Let’s try 1B. 1B is 2(-3+4). Now in the order of operations, anything that’s in the parenthesis is done first. So first, we’ll solve the parenthesis, (-3+4) = +1, 4-3=1, so 2*1=2. So, that’s how we do the order of operation when it comes to multiplication and addition in this case. Now let’s do the second problem. Second problem says that a student puts in $25.00 each time he makes a deposit. So every deposit is $25.00, and he takes out $20.00 each time he makes a withdrawal. So every withdrawal is $20.00. If he makes two deposits and four withdraws, what is the net change in the student account? What we need to find out is what does the account change by? So let’s do this problem slightly differently. Second problem says that each deposit equals $25.00. So the result of every deposit or the resulting change from one deposit equals plus $25.00, because we are adding $25.00 every time he makes a deposit. So the resulting change in the account from one deposit is $25.00 positive. Now with withdrawal, $20.00, he takes out $20.00 each time. So the resulting change from one withdrawal equals (-$20.00), and the reason its negative is because his money has been taken out. So that’s the two things that we know. The problem tells us that he made two deposits and four withdrawals. So let’s solve this. So he made two deposits and four withdrawals. So the change from two deposits equals two times the change from one deposit which is $25.00, which is $50.00 as the total change from two deposits. Now, from four withdrawals, so the change from four withdrawals equals four times $20.00 but this is a negative. (-$20.00)*4, which is negative times positive is a negative, $80.00. So change from four withdrawals is $80.00. Change from two deposits is $50.00. This is a positive and this is a negative. So the net change from both of these equals this plus this. $50.00+ (-$80.00), 50-80 is the same as 50+ (-80) = (-$30.00). So the net change is a lost of $30 or reduction of $30.00. Net change is $30 coming out of the account or a -$30.00.
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