EXAMPLES
Ex 1:
What will be the sign of the product if we multiply together 199 negative and 10 positive integers?
Sol:
Whatever may be the number of positive integers, it will not affect the sign of the product.
Since 199 is odd and the product of an odd number of a negative integer is negative, So the given product is negative.
Ex 2:
In a class test containing 20 questions, 4 marks are given for every correct answer and (– 2) marks are given for every incorrect answer. Ranjita attempts all questions and 12 of her answers are correct. What is her total score?
Sol:
| Marks given for 1 correct answer | = | 4 |
| Marks given for 12 correct answers | = | (4 × 12) |
| = | 48 | |
| Marks given for 1 incorrect answer | = | – 2 |
| Marks given for (20 – 12) i.e., 8 incorrect answers | = | (– 2) × 8 |
| = | – 16 | |
| Ranjita's total score | = | 48 + (– 16) |
| = | 32 |
Ex 3:
A shopkeeper gains Rs.1 on each pen and loses 40 paise on each pencil. He sells 45 pens and some pencils losing Rs.5 in all. How many pencils does he sell?
Sol:
| Sol: Suppose he sells x pencils. | ||
| Total gain on pen | = | Rs.45 |
| Total loss on pencils | = | Rs.  |
| = | Rs. x |
|
| ∴ 45 – x |
= | 5 |
| ⇒ x |
= | (45 - 5) |
| ⇒ x |
= | 40 |
| ⇒ x | = |  |
| = | 100 | |
| Hence, the number of pencils sold is 100. |