Exercise: 3-C
Mental Maths
Q1: Fill in the blanks:
i. -36 + 8 = ?
We are adding a positive number to a negative number:
-36 + 8 = -28
Correct Answer: -28
ii. -36 – 8 = ?
Subtracting a positive number from a negative number means moving more left on number line:
-36 – 8 = -44
Correct Answer: -44
iii. -46 – (-6) = ?
Subtracting a negative is same as adding a positive:
-46 – (-6) = -46 + 6 = -40
Correct Answer: -40
iv. 53 – (-10) = ?
Again, subtracting a negative is same as adding the positive value:
53 – (-10) = 53 + 10 = 63
Correct Answer: 63
v. 0 – (-13) = ?
0 – (-13) = 0 + 13 = 13
Correct Answer: 13
vi. 9 + 1 – 61 = ?
Step 1: 9 + 1 = 10
Step 2: 10 – 61 = -51
Correct Answer: -51
Q2: Write T for true and F for false statement:
i. 0 is a positive integer.
0 is neither positive nor negative.
Correct Answer: False
ii. 10°C below freezing point can be expressed as (-10°C).
Yes, temperature below zero is expressed using negative sign.
Correct Answer: True
iii. -(-15) = +15
Double negative becomes positive:
-(-15) = 15
Correct Answer: True
iv. Predecessor of (-9) is -10.
Yes, number just before -9 is -10.
Correct Answer: True
v. On subtracting -40 from 40, we get 80.
40 – (-40) = 40 + 40 = 80
Correct Answer: True
vi. Successor of -1 is 0.
Number just after -1 is 0.
Correct Answer: True
vii. |-15| + 10 = -5
|-15| = 15
15 + 10 = 25 ≠ -5
Correct Answer: False
