Ceci's ScribePost

multiplying integers

when the integers have different value, ( - or + ) the product is negative.

when the integers have same value, ( -,+ )the product is positive.
when multiplying integers, count the negative signs
odd number = negative
even number = positive

8.2 textbook

 10. Estimate and then calculate
    1)  (+17) * (-24) = 408
 est:  (+20) * (-24) = -480
I changed 17 to 20 because 17 is close to 20, also i can calculate 20 * 24 in my head fast. 
Then i used the sign rule to solve this question, when the integers have different value, the product is negative.

  2)  (+37) * (+22) = 814
est: (+40) * (+22) =880 
 I changed 37 to 40 because 37 is close to 40, also i can calculate 40 * 22 in my head fast. 
Then i used the sign rule to solve this question, when the integers have same value, the product is positive.

  3)  (-72) * (+15) =  -1080 
est: (-70) * (+15) = 1050

I changed 72 to 70 because 72 is close to 70, also i can calculate 70 * 15 in my head fast. 
Then i used the sign rule to solve this question, when the integers have different value, the product is negative.

 4)   (-28) * (-47) = 1316
est: (-30) * (-45) = 1350

I changed 28 to 30, 47 to 45 because 28 is close to 30,and 47 is close to 45 also i can calculate 30 * 45 in my head fast. Then i used the sign rule to solve this question, when the integers have same value, the product is positive.






12. A telephone company offer its customer a $15 discount per month if they also sign up for internet service. how much is the annual discount?
     (+12) * (-15) = -180
     12 groups of (-15)
    12 month of $15.00 off
I used negative sign for $15 because discount means off (getting 15 dollars off each month)
annual means one year, there are 12 months in a year, and we have $15.00 off each year. 
so we need to calculate how much is the annual discount, we multiply 12 by -15 because we have 12 groups of -15. Then we use the sign rule to solve this question, when the integers have different value, the product is negative. 12 * 15 equals 180, the answer has to be negative so, it is -180.



13. A hot air balloon is descending at 60 m/min. how far does it descend in 25 min?
        (+25) * (-60) = -1500 
       25 groups of (-60)
      25 min of 60 m/ min
I used negative sign for 60 m because descend means going down, the hot air balloon is going down 60 m/ min.
The hot air balloon is descending at 60 m/min, and the question ask how far does it descend in 25 min? that means, we have 25 groups of 60 because , 60 m/ min, and there are 25 of them. To solve this question we need to multiply 25 by (-60). we can use the sign rule to solve this question, when the integers have different value, the product is negative.  25 * 60 = 1500, the answer has to be negative so it is 



                                                                                                                                                                                                                                         




here is a video that can help you with multiplying integers (with the chip model)
multiplying integers is not hard, you can do it!
hope my scribe can help you!