Arithmetic Expressions | A

Question 3

Context: Let us consider the expression (7)+10+(11)(-7) + 10 + (-11) again. What happens when we change the order and add 7-7 and 11-11 first, and then add this sum to 1010? Will we get the same sum as before? We see that adding the terms of the expression (7)+10+(11)(-7) + 10 + (-11) in any order gives the same sum of 8-8.

Q. Does adding the terms of an expression in any order give the same value? Take some more expressions and check. Consider expressions with more than 3 terms also.

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Solution
Understand the Question
  • Addition of integers follows both the commutative property (a+b=b+aa + b = b + a) and the associative property ((a+b)+c=a+(b+c)(a + b) + c = a + (b + c)).
  • This means the terms of an expression can be rearranged, grouped, or added in any order without changing the final sum.
  • We will verify this property by reordering the terms in the given expression, testing a new 3-term expression, and testing an expression with 4 terms.

Step 1 · Verify with the Given Expression

Given expression: (7)+10+(11)(-7) + 10 + (-11)

Adding the negative numbers first

(7)+(11)=(7+11)=18\begin{aligned} (-7) + (-11) &= -(7 + 11) \\ &= -18 \end{aligned}

Adding this result to 1010

10+(18)=1018=(1810)=8\begin{aligned} 10 + (-18) &= 10 - 18 \\ &= -(18 - 10) \\ &= -8 \end{aligned}

The sum is 8-8, which is the same as the original sum.

Step 2 · Test with Another 3-Term Expression

Consider the expression 5+(3)+85 + (-3) + 8.

Order 1: Left to right

5+(3)=53=2\begin{aligned} 5 + (-3) &= 5 - 3 \\ &= 2 \end{aligned}

2+8=102 + 8 = 10

Order 2: Adding 55 and 88 first 5+8=135 + 8 = 13

13+(3)=133=10\begin{aligned} 13 + (-3) &= 13 - 3 \\ &= 10 \end{aligned}

Both orders produce the same sum of 1010.

Step 3 · Test with an Expression Having More Than 3 Terms

Consider the 4-term expression 2+(4)+6+(1)2 + (-4) + 6 + (-1).

Order 1: Left to right

2+(4)=24=2\begin{aligned} 2 + (-4) &= 2 - 4 \\ &= -2 \end{aligned}

2+6=4-2 + 6 = 4

4+(1)=41=3\begin{aligned} 4 + (-1) &= 4 - 1 \\ &= 3 \end{aligned}

Order 2: Grouping positive and negative terms 2+6=82 + 6 = 8

(4)+(1)=(4+1)=5\begin{aligned} (-4) + (-1) &= -(4 + 1) \\ &= -5 \end{aligned} 8+(5)=85=3\begin{aligned} 8 + (-5) &= 8 - 5 \\ &= 3 \end{aligned}

Both orders yield the same result of 33.

Answer

Yes, adding the terms of an expression in any order gives the same value.

Common Mistakes
  • Sign Errors with Negative Numbers: Forgetting that adding two negative numbers yields a negative number with their magnitudes added, e.g., (7)+(11)=18(-7) + (-11) = -18, not 4-4.
  • Sign of the Difference: When adding numbers with opposite signs, the sign of the larger absolute value is taken, e.g., 10+(18)=(1810)=810 + (-18) = -(18 - 10) = -8.

More questions in A

Q1

Context: In an expression having two terms, swapping them does not change the value:

Term 1+Term 2=Term 2+Term 1\text{Term 1} + \text{Term 2} = \text{Term 2} + \text{Term 1}

Q. Can you explain why this is happening using the Token Model of integers that we saw in the Class 6 textbook of mathematics?

Q3

Context: Let us consider the expression (7)+10+(11)(-7) + 10 + (-11) again. What happens when we change the order and add 7-7 and 11-11 first, and then add this sum to 1010? Will we get the same sum as before? We see that adding the terms of the expression (7)+10+(11)(-7) + 10 + (-11) in any order gives the same sum of 8-8.

Q. Does adding the terms of an expression in any order give the same value? Take some more expressions and check. Consider expressions with more than 3 terms also.

Q4

Context: Does adding the terms of an expression in any order give the same value? Take some more expressions and check. Consider expressions with more than 33 terms also.

Q. Can you explain why this is happening using the Token Model of integers that we saw in the Class 6 textbook of mathematics?

Q5

What happens to the value of an expression if we increase or decrease the value of one of its terms?

Some expressions are given in following three columns. In each column, one or more terms are changed from the first expression. Go through the example (in the first column) and fill the blanks, doing as little computation as possible.

Q6

Expression Engineer!

Using three 3's along with the four operations (addition, subtraction, multiplication, and division) and brackets as needed we can create several expressions. For example, 3+33=2\dfrac{3 + 3}{3} = 2, 3+33=33 + 3 - 3 = 3, 3×3+3=123 \times 3 + 3 = 12, and so on.

  • Using four 4's, create expressions to get all values from 1 to 20.
  • Using the numbers 1, 2, 3, 4, and 5 exactly once in any order get as many values as possible between 10-10 and +10+10.
  • Using the numbers 0 to 9 exactly once in any order, make an expression with a value 100.
  • What other similar interesting questions can you ask?
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