Multiply And Divide Integers

Money that you save in a bank account is positive.

Money that you owe is negative.

The SPUN rule for multiplying and dividing positive and negative integers.

Same signs Positive answer
Unlike or different signs Negative answer


Multiplying integers with the same signs gives a positive answer
+2 × +3 = +6
–2 × –3 = +6

Dividing integers with the same signs gives a positive answer
–10 ÷ –2 = +5
–6 ÷ –3 = +2

Multiplying integers with unlike (different signs) gives a negative answer
–6 × +3 = –18
+5 × –2 = –10

Dividing integers with unlike (different signs) gives a negative answer
–10 ÷ +5 = –2
+12 ÷ –4 = –3


Example One

Babette saves $5 every week for 10 weeks. Write this with integers and then find the total saved.

Answer:
+5 × +10 = +50 = $50


Example Two

Bob receives 3 bills for $4 each. Write this with integers and then find the total owed.

Answer:
–4 x +3 = –12 = $12 owed


Example Three

Mike owes a total of $100. He will repay this over 10 weeks. How much will be paid each week?

Answer:
–100 ÷ +10 = –10 = $10 repaid weekly


Example Four

+3 × –4 × +10 ÷ –5

Answer:
Calculate this from left to right.
+3 × –4 × +10 ÷ –5
= –12 × +10 ÷ –5
= –120 ÷ –5
= +24

Questions

Q1. +5 × –2 × –3
Q2. –20 × –4 ÷ –5

Answers
A1. +30
A2. –16