Question 5
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.

Changing a term in an addition changes the sum by the same amount.
Step 1 — Column 1 Calculations
We start with the first expression. The sum of 53 and -16 is 37.
Next, we look at the second expression. The first number, 54, is one more than 53. The second number, -16, stays the same. So, the sum will be one more than 37.
Now, we consider the third expression. The first number, 53, stays the same. The second number is -15. We compare -15 with -16. -15 is one more than -16. So, the sum will be one more than 37.

Step 2 — Column 2 Calculations
We use the first expression again. The sum of 53 and -16 is 37.
Next, we look at the second expression. The first number, 52, is one less than 53. The second number, -16, stays the same. So, the sum will be one less than 37.
Now, we consider the third expression. The first number, 53, stays the same. The second number is -17. We compare -17 with -16. -17 is one less than -16. So, the sum will be one less than 37.

Step 3 — Column 3 Calculations
Let us find the sum for the first expression. We add -87 and -16.
Next, we look at the second expression. The first number, -88, is one less than -87. The second number, -15, is one more than -16. One term decreased by 1. The other term increased by 1. The total change to the sum is zero. So, the sum remains the same.
Now, we consider the third expression. The first number, -86, is one more than -87. The second number, -18, is two less than -16. One term increased by 1. The other term decreased by 2. The total change to the sum is . So, the sum will be one less than -103.
Finally, we look at the fourth expression. The first number, -97, is ten less than -87. The second number, -26, is ten less than -16. One term decreased by 10. The other term decreased by 10. The total change to the sum is . So, the sum will be twenty less than -103.

Answer
(i) Column 1, second expression: 38 (ii) Column 1, third expression: 38 (iii) Column 2, second expression: 36 (iv) Column 2, third expression: 36 (v) Column 3, first expression: -103 (vi) Column 3, second expression: -103 (vii) Column 3, third expression: -104 (viii) Column 3, fourth expression: -123
More questions in A
Context: In an expression having two terms, swapping them does not change the value:
Q. Can you explain why this is happening using the Token Model of integers that we saw in the Class 6 textbook of mathematics?
Context: Let us consider the expression again. What happens when we change the order and add and first, and then add this sum to ? Will we get the same sum as before? We see that adding the terms of the expression in any order gives the same sum of .
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.
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 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?
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.
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, , , , 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 and .
- 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?