Operations with Integers | FIO

Question 19

An alien society uses a peculiar currency called 'pibs' with just two denominations of coins — a+13 pibs coin and a -9 pibs coin. You have several of these coins. Is it possible to purchase an item that costs +85 pibs?

Solution

We need to find if we can combine the values of the coins to make exactly +85 pibs.

Step 1 — Set up the equation

Let us use $x$ for the number of +13 pibs coins. Let us use $y$ for the number of -9 pibs coins. We want to find non-negative integers for $x$ and $y$ . The total value must be +85 pibs. So, we write an equation for the total value.

$13x - 9y = 85$

Step 2 — Find a solution

We need to find values for $x$ and $y$ . These values must be zero or positive whole numbers. Let us try different values for $x$ . If we try $x = 10$ :

$13 \times 10 - 9y = 85$

$130 - 9y = 85$

We want to find $y$ . We subtract 130 from both sides.

$-9y = 85 - 130$

$-9y = -45$

Now, we divide both sides by -9.

$y = \frac{-45}{-9}$

$y = 5$

$\boxed{x = 10, y = 5}$

Step 3 — Verify the solution

We found that $x = 10$ and $y = 5$ . Both these numbers are positive whole numbers. This means we can use 10 coins of +13 pibs. We can also use 5 coins of -9 pibs. Let us calculate the total value with these coins.

$10 \times 13 + 5 \times (-9)$

$= 130 - 45$

$= 85$

$\boxed{\text{Total value} = +85 \text{ pibs}}$

The total value is exactly +85 pibs. So, it is possible to purchase the item.

Answer

Yes, it is possible to purchase an item that costs +85 pibs.

More questions in FIO

Let us try to find a few more pairs of numbers from their sums and differences:

(a) Sum = 27, Difference = 9

(b) Sum = 4, Difference = 12

(d) Sum = 0, Difference = -10

(e) Sum = -7, Difference = -1

(f) Sum = -7, Difference = -13

Using the token interpretation, find the values of:

(a) $3 \times (-2)$

(b) $(-5) \times (-2)$

(d) $(-7) \times 3$

If $123 \times 456 = 56088$ , without calculating, find the value of:

(a) $(-123) \times 456$

(b) $(-123) \times (-456)$

Try to frame a simple rule to multiply two integers.

Consider the numbers represented by the following tokens in the diagram:

Find the following products.

(a) $4 \times (-3)$

(b) $(-6) \times (-3)$

(d) $(-8) \times 4$

(e) $(-9) \times 10$

(f) $10 \times (-17)$

Find the values of:

(a) $14 \times (-15)$

(b) $-16 \times (-5)$

(d) $(-46) \div (-23)$

A freezing process requires that the room temperature be lowered from $32^\circ\text{C}$ at the rate of $5^\circ\text{C}$ every hour. What will be the room temperature 10 hours after the process begins?

A cement company earns a profit of ₹8 per bag of white cement sold and a loss of ₹5 per bag of grey cement sold. [Represent the profit/loss as integers.]

(a) The company sells 3,000 bags of white cement and 5,000 bags of grey cement in a month. What is its profit or loss? (b) If the number of bags of grey cement sold is 6,400 bags, what is the number of bags of white cement the company must sell to have neither profit nor loss?

Replace the blank with an integer to make a true statement.

(a) $(-3) \times \underline{\quad\quad} = 27$

(b) $5 \times \underline{\quad\quad} = (-35)$

(d) $\underline{\quad\quad} \times (-12) = 132$

(e) $\underline{\quad\quad} \div (-8) = 7$

(f) $\underline{\quad\quad} \div 12 = -11$

Q10

Find the values of the following expressions: (a) $(-5) \times (18 + (-3))$ (b) $(-7) \times 4 \times (-1)$ (c) $(-2) \times (-1) \times (-5) \times (-3)$

Q11

Find the values of the following expressions:

(a) $(-27) \div 9$

(b) $84 \div (-4)$

Q12

Find the integer whose product with $(-1)$ is:

(a) 27

(b) -31

(d) 1

(e) 0

Q13

If $47 - 56 + 14 - 8 + 2 - 8 + 5 = -4$ , then find the value of $-47 + 56 - 14 + 8 - 2 + 8 - 5$ without calculating the full expression.

Q14

Do you remember the Collatz Conjecture from last year? Try a modified version with integers. The rule is — start with any number; if the number is even, take half of it; if the number is odd, multiply it by $-3$ and add 1; repeat. An example sequence is shown below.

Try this with different starting numbers: $(-21)$ , $(-6)$ , and so on. Describe the patterns you observe.

Q15

In a test, (+4) marks are given for every correct answer and (-2) marks are given for every incorrect answer.

(a) Anita answered all the questions in the test. She scored 40 marks even though 15 of her answers were correct. How many of her answers were incorrect? How many questions are in the test?

(b) Anil scored (-10) marks even though he had 5 correct answers. How many of his answers were incorrect? Did he leave any questions unanswered?

Q16

Pick the pattern — find the operations done by the machine shown below.

Q17

Imagine you're in a place where the temperature drops by 5°C each hour. If the temperature is currently at 8°C, write an expression which denotes the temperature after 4 hours.

Q18

Find 3 consecutive numbers with a product of (a) -6, (b) 120.

Q19

Q20

Find the values of:

(a) $(32 \times (-18)) \div ((-36))$

(b) $(32) \div ((-36) \times (-18))$

(d) $(280 \times (-7)) \div ((-8) \times (-35))$

Q21

Arrange the expressions given below in increasing order:

(a) $(-348) + (-1064)$

(b) $(-348) - (-1064)$

(d) $(-348) \times (-1064)$

(e) $348 \times (-1064)$

(f) $348 \times 964$

Q22

Given that $(-548) \times 972 = -532656$ , write the values of:

(a) $(-547) \times 972$

(b) $(-548) \times 971$

Q23

Given that $207 \times (-33 + 7) = -5382$ , write the value of $-207 \times (33 - 7) =\_\_\_?$

Q24

Use the numbers $3, -2, 5, -6$ exactly once and the operations '+', '-', and 'x' exactly once and brackets as necessary to write an expression such that —

(a) the result is the maximum possible

(b) the result is the minimum possible

Q25

Fill in the blanks in at least 5 different ways with integers:

(a) $\square + \square \times \square = -36$

(b) $(\square - \square) \times \square = 12$