Solve the Equation: (-5)·(?4)=20 - Determining the Missing Sign

Integer Multiplication with Missing Signs

Fill in the corresponding sign for the following question

(5)(?4)=20 (-5)\cdot(?4)=20

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Step-by-step video solution

Watch the teacher solve the problem with clear explanations
00:00 Complete the appropriate sign
00:04 The solution is positive, so we want a sign that leads to a positive result
00:09 Negative times negative always equals positive
00:14 Therefore the appropriate sign is negative
00:18 And this is the solution to the question

Step-by-step written solution

Follow each step carefully to understand the complete solution
1

Understand the problem

Fill in the corresponding sign for the following question

(5)(?4)=20 (-5)\cdot(?4)=20

2

Step-by-step solution

We must first consider what value we need to multiply by a negative number in order to obtain a positive number.

Let's remember the rule:

(x)×(x)=+x (-x)\times(-x)=+x

Therefore, the answer is:

4 -4

3

Final Answer

() (-)

Key Points to Remember

Essential concepts to master this topic
  • Sign Rule: Negative times negative equals positive result
  • Technique: Since (-5) × ? = 20 (positive), ? must be negative
  • Check: Verify (-5) × (-4) = 20 gives positive 20 ✓

Common Mistakes

Avoid these frequent errors
  • Assuming the missing number must be positive
    Don't think (+4) works because 4 is the number shown = (-5) × (+4) = -20, not +20! This ignores sign rules for multiplication. Always remember: negative × negative = positive, so the missing sign must be negative.

Practice Quiz

Test your knowledge with interactive questions

Solve the following exercise:

\( (+6)\cdot(+9)= \)

FAQ

Everything you need to know about this question

Why can't the missing sign be positive?

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Because (5)×(+4)=20 (-5) \times (+4) = -20 , not +20! When you multiply a negative by a positive, you always get a negative result.

How do I remember the sign rules for multiplication?

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Use this simple pattern: Same signs = Positive, Different signs = Negative. So negative × negative = positive, but negative × positive = negative.

What if I see a question mark in front of a number?

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The question mark represents a missing sign (+ or -), not a missing number. The number itself (like 4) is already given - you just need to determine if it's positive or negative.

How can I check my answer quickly?

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Simply multiply your complete answer: (5)×(4)=+20 (-5) \times (-4) = +20 . If this equals the right side of the equation, you're correct!

Do parentheses around numbers always mean they're negative?

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Not always! Parentheses like (-5) show the number is negative, but (?4) means we need to find the sign. The parentheses just group the sign with the number.

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