High School

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Exercise 4.1.5

1. If [tex]\( y \propto \frac{1}{x} \)[/tex] and [tex]\( y = 6 \)[/tex] when [tex]\( x = 4 \)[/tex], then find the constant of proportionality.

2. [tex]\( y \)[/tex] is inversely proportional to [tex]\( x \)[/tex]. If [tex]\( x = 25 \)[/tex] and [tex]\( y = 8 \)[/tex], what is the value of [tex]\( y \)[/tex] when [tex]\( x = 10 \)[/tex]?

3. Which of the following tables shows an inverse proportional relationship between [tex]\( x \)[/tex] and [tex]\( y \)[/tex]?

a.
[tex]\[
\begin{tabular}{|c|c|c|c|}
\hline
$x$ & 2 & 4 & 8 \\
\hline
$y$ & 36 & 18 & 9 \\
\hline
\end{tabular}
\][/tex]

b.
[tex]\[
\begin{tabular}{|c|c|c|c|}
\hline
$x$ & 5 & 10 & 15 \\
\hline
$y$ & 20 & 10 & 5 \\
\hline
\end{tabular}
\][/tex]

4. It takes 8 days for 35 laborers to harvest coffee on a plantation. How long will 20 laborers take to harvest coffee on the same plantation?

5. [tex]\( x \)[/tex] is inversely proportional to [tex]\( y \)[/tex]. If [tex]\( x = 25 \)[/tex] and [tex]\( y = 15 \)[/tex], find [tex]\( y \)[/tex] when [tex]\( x = 30 \)[/tex].

6. 100 men working in a factory produce 6000 articles in 10 days. How long will it take (assume all workers do the job at the same rate):

a. 50 men to produce 6000 articles?

b. 150 men to produce 6000 articles?

7. A contractor appoints 36 workers to build a wall. They could finish the task in 12 days. How many days will 16 workers take to finish the same task?

Answer :

Sure! Let's solve each part of the exercise one step at a time.

1. Find the constant of proportionality:

We know that [tex]\( y \propto \frac{1}{x} \)[/tex], which implies [tex]\( y = \frac{k}{x} \)[/tex] where [tex]\( k \)[/tex] is the constant of proportionality.

Given [tex]\( y = 6 \)[/tex] when [tex]\( x = 4 \)[/tex]:
[tex]\[
6 = \frac{k}{4}
\][/tex]
Solving for [tex]\( k \)[/tex], we get:
[tex]\[
k = 6 \times 4 = 24
\][/tex]

2. Find the value of [tex]\( y \)[/tex] when [tex]\( x = 10 \)[/tex]:

Since [tex]\( y \)[/tex] is inversely proportional to [tex]\( x \)[/tex], we have [tex]\( y \times x = \text{constant} \)[/tex].

Given [tex]\( x = 25 \)[/tex] and [tex]\( y = 8 \)[/tex]:
[tex]\[
y \times 25 = 8 \times 25 = 200
\][/tex]

Now, find [tex]\( y \)[/tex] when [tex]\( x = 10 \)[/tex]:
[tex]\[
y \times 10 = 200 \implies y = \frac{200}{10} = 20
\][/tex]

3. Which table shows an inverse proportional relationship?

For an inverse proportional relationship, the product [tex]\( x \times y \)[/tex] should be constant.

- Table (a):
[tex]\[
\begin{aligned}
2 \times 36 & = 72, \\
4 \times 18 & = 72, \\
8 \times 9 & = 72.
\end{aligned}
\][/tex]
Constants are equal, so Table (a) shows an inverse proportional relationship.

- Table (b):
[tex]\[
\begin{aligned}
5 \times 20 & = 100, \\
10 \times 10 & = 100, \\
15 \times 5 & = 75.
\end{aligned}
\][/tex]
Constants are not equal, so Table (b) does not.

4. How long will 20 laborers take to harvest coffee?

Using the inverse relationship between laborers and days:
[tex]\[
\text{Days taken by 20 laborers} = \frac{35 \times 8}{20} = 14 \text{ days}
\][/tex]

5. Find [tex]\( y \)[/tex] when [tex]\( x = 30 \)[/tex]:

Given [tex]\( x = 25 \)[/tex] and [tex]\( y = 15 \)[/tex]:
[tex]\[
25 \times 15 = 375
\][/tex]

New [tex]\( x = 30 \)[/tex]:
[tex]\[
y \times 30 = 375 \implies y = \frac{375}{30} = 12.5
\][/tex]

6. How long will 50 and 150 men take?

- 50 men:
[tex]\[
\text{Days needed} = \frac{100 \times 10}{50} = 20 \text{ days}
\][/tex]

- 150 men:
[tex]\[
\text{Days needed} = \frac{100 \times 10}{150} \approx 6.67 \text{ days}
\][/tex]

7. How many days will 16 workers take?

Using the inverse relation for workers and days:
[tex]\[
\text{Days for 16 workers} = \frac{36 \times 12}{16} = 27 \text{ days}
\][/tex]

And that's how you can solve each part of the exercise step by step!

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