12 multiple-choice questions, progressively harder.
What is (−6)×(−2)×(−3)(-6) \times (-2) \times (-3)(−6)×(−2)×(−3)?
Solution
Correct answer: D
Multiply the sizes and count the negatives. The sizes give 6×2×3=366 \times 2 \times 3 = 366×2×3=36, and there are three negative factors, an odd count.
(−6)×(−2)×(−3)=−36(-6) \times (-2) \times (-3) = -36(−6)×(−2)×(−3)=−36
An odd number of negatives makes the product negative.
What is (−7)×(−6)−3\dfrac{(-7) \times (-6)}{-3}−3(−7)×(−6)?
Evaluate the numerator first. The product (−7)×(−6)=42(-7) \times (-6) = 42(−7)×(−6)=42 is positive.
42−3=−14\frac{42}{-3} = -14−342=−14
The top is positive and the bottom is negative, so the quotient is negative; 42÷3=1442 \div 3 = 1442÷3=14.
What is (−100)÷(−4)÷(−5)(-100) \div (-4) \div (-5)(−100)÷(−4)÷(−5)?
Correct answer: C
Work left to right. First (−100)÷(−4)=25(-100) \div (-4) = 25(−100)÷(−4)=25, since the signs match. Then divide by −5-5−5; those signs differ, so the quotient is negative.
25÷(−5)=−525 \div (-5) = -525÷(−5)=−5
Which expression has the smallest (most negative) value?
Evaluate each. The first is 202020, the second is −21-21−21, the third is −24-24−24, and the fourth is −20-20−20.
6×(−4)=−246 \times (-4) = -246×(−4)=−24
The smallest value is the most negative one, and −24-24−24 lies farther left than −21-21−21, −20-20−20, or 202020, so the third expression is smallest.
If a=−5a = -5a=−5 and b=4b = 4b=4, what is a×b÷(−2)a \times b \div (-2)a×b÷(−2)?
Correct answer: B
Substitute and work left to right. First a×b=(−5)×4=−20a \times b = (-5) \times 4 = -20a×b=(−5)×4=−20.
(−20)÷(−2)=10(-20) \div (-2) = 10(−20)÷(−2)=10
Dividing −20-20−20 by −2-2−2 gives a positive result because the signs match.
What is (−1)×2×(−3)×4×(−1)(-1) \times 2 \times (-3) \times 4 \times (-1)(−1)×2×(−3)×4×(−1)?
Multiply the sizes and count the negatives. The sizes give 1×2×3×4×1=241 \times 2 \times 3 \times 4 \times 1 = 241×2×3×4×1=24, and there are three negative factors, an odd count.
(−1)×2×(−3)×4×(−1)=−24(-1) \times 2 \times (-3) \times 4 \times (-1) = -24(−1)×2×(−3)×4×(−1)=−24
What is −546×(−3)\dfrac{-54}{6} \times (-3)6−54×(−3)?
Work left to right. First −546=−9\frac{-54}{6} = -96−54=−9, since the signs differ.
(−9)×(−3)=27(-9) \times (-3) = 27(−9)×(−3)=27
Then multiplying two negatives gives the positive result 272727.
What is 8×(−3)−(−6)×48 \times (-3) - (-6) \times 48×(−3)−(−6)×4?
Correct answer: A
Multiply before subtracting. The products are 8×(−3)=−248 \times (-3) = -248×(−3)=−24 and (−6)×4=−24(-6) \times 4 = -24(−6)×4=−24.
−24−(−24)=−24+24=0-24 - (-24) = -24 + 24 = 0−24−(−24)=−24+24=0
Subtracting −24-24−24 adds 242424, which cancels the first term to give 000.
The product of three integers is positive. Which of these is possible for the number of negative factors among them?
Each negative factor flips the sign once, so a positive product needs an even count of negative factors. Two negatives flip the sign twice, which lands back where it started.
(−2)×(−3)×5=30(-2) \times (-3) \times 5 = 30(−2)×(−3)×5=30
Three integers can carry 000, 111, 222 or 333 negatives, and only an even count gives a positive product. Of the choices, exactly 222 is the even one, so two negative factors is possible.
What is (−8)×(−9)−12\dfrac{(-8) \times (-9)}{-12}−12(−8)×(−9)?
Evaluate the numerator first. The product (−8)×(−9)=72(-8) \times (-9) = 72(−8)×(−9)=72 is positive.
72−12=−6\frac{72}{-12} = -6−1272=−6
The top is positive and the bottom is negative, so the quotient is negative; 72÷12=672 \div 12 = 672÷12=6.
What is −72−9−3×(−4)\dfrac{-72}{-9} - 3 \times (-4)−9−72−3×(−4)?
Evaluate the quotient and the product first. The quotient −72−9=8\frac{-72}{-9} = 8−9−72=8 and the product 3×(−4)=−123 \times (-4) = -123×(−4)=−12.
8−(−12)=8+12=208 - (-12) = 8 + 12 = 208−(−12)=8+12=20
Subtracting the negative −12-12−12 adds 121212, giving 202020.
What is (−3)×4×(−2)−8\dfrac{(-3) \times 4 \times (-2)}{-8}−8(−3)×4×(−2)?
Evaluate the numerator first. The factors give (−3)×4=−12(-3) \times 4 = -12(−3)×4=−12, then (−12)×(−2)=24(-12) \times (-2) = 24(−12)×(−2)=24.
24−8=−3\frac{24}{-8} = -3−824=−3
The top is positive and the bottom is negative, so the quotient is negative; 24÷8=324 \div 8 = 324÷8=3.
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