High School

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II. Choose the correct answer from the given alternatives.

9. In a school, [tex]58 \%[/tex] of the total number of students are boys. If the number of boys is 840, how many students are there in the school?

a. 2000
b. 1800
c. 1500
d. 2100

10. Birr 300 is invested at [tex]6 \%[/tex] simple interest per annum. How long will it take for the interest to be Birr 180?

a. 12 years
b. 10 years
c. 8 years
d. 24 years

11. The decimal form of [tex]\frac{3}{4} \%[/tex] is:

a. 0.75
b. 0.075
c. 0.0075
d. 0.057

12. The simple interest on Birr 400 invested for 4 months was Birr 12. What is the annual (yearly) rate of interest?

a. [tex]36 \%[/tex]
b. [tex]4.8 \%[/tex]
c. [tex]7 \%[/tex]
d. [tex]9 \%[/tex]

13. If [tex]a, b,[/tex] and [tex]c[/tex] are numbers such that [tex]a: b: c=1: 3: 4[/tex] and [tex]c=28[/tex], then the sum of [tex]a+b+c[/tex] is:

a. 56
b. 60
c. 72
d. 84

Answer :

Sure, let's go through each question step-by-step:

9. Finding the total number of students:

We know that 58% of the total number of students are boys, and there are 840 boys in the school. To find the total number of students, we set up the equation:

[tex]\[ 0.58 \times \text{Total Students} = 840 \][/tex]

To find the total number of students, divide both sides by 0.58:

[tex]\[ \text{Total Students} = \frac{840}{0.58} \approx 1448 \][/tex]

So, the total number of students in the school is approximately 1448. Since this doesn't exactly match any of the multiple-choice options, let's assume the closest correct choice should be selected. However, given this estimate, it might have been a typo in the options.

10. Time for the interest to reach 180 Birr:

The simple interest formula is:

[tex]\[ \text{Interest} = \text{Principal} \times \text{Rate} \times \text{Time} \][/tex]

Given:
- Principal = 300 Birr
- Rate = 6% or 0.06
- Interest = 180 Birr

To find the time, rearrange the formula:

[tex]\[ \text{Time} = \frac{\text{Interest}}{\text{Principal} \times \text{Rate}} = \frac{180}{300 \times 0.06} = 10 \][/tex]

It will take 10 years for the interest to become 180 Birr.

11. Decimal form of [tex]\(\frac{3}{4}\%\)[/tex]:

First, convert [tex]\(\frac{3}{4}\%\)[/tex] into its decimal form:

1. [tex]\(\frac{3}{4}\% = \frac{3}{4} \times \frac{1}{100}\)[/tex]

2. [tex]\(\frac{3}{4} = 0.75\)[/tex]

3. [tex]\(0.75 \times 0.01 = 0.0075\)[/tex]

The decimal form is 0.0075.

12. Annual interest rate:

The formula for simple interest is given by:

[tex]\[ \text{Interest} = \text{Principal} \times \text{Rate} \times \text{Time} \][/tex]

Given:
- Principal = 400 Birr
- Interest = 12 Birr
- Time = 4 months (which is [tex]\(\frac{1}{3}\)[/tex] of a year)

To find the annual rate, we use:

[tex]\[ \text{Rate} = \frac{\text{Interest}}{\text{Principal} \times \text{Time}} = \frac{12}{400 \times \frac{1}{3}} \][/tex]

Multiply by 3 to adjust for annual rate:

[tex]\[ \text{Rate} = \frac{12 \times 3}{400} \][/tex]

Convert into percentage by multiplying by 100:

[tex]\[ \text{Rate} = \left(\frac{36}{400}\right) \times 100 = 9\% \][/tex]

The annual interest rate is 9%.

13. Sum of [tex]\(a + b + c\)[/tex]:

Given the ratio [tex]\(a:b:c = 1:3:4\)[/tex] and [tex]\(c = 28\)[/tex],

Convert the ratio into real numbers:
- Let [tex]\(a = x\)[/tex], [tex]\(b = 3x\)[/tex], [tex]\(c = 4x\)[/tex].

Since [tex]\(c = 28\)[/tex], [tex]\[4x = 28\][/tex]

Calculate [tex]\(x\)[/tex]:

[tex]\[ x = \frac{28}{4} = 7\][/tex]

Substitute [tex]\(x\)[/tex] to find [tex]\(a, b, c\)[/tex]:

- [tex]\(a = 7\)[/tex]
- [tex]\(b = 3 \times 7 = 21\)[/tex]
- [tex]\(c = 4 \times 7 = 28\)[/tex]

The sum is:

[tex]\[ a + b + c = 7 + 21 + 28 = 56 \][/tex]

The sum of [tex]\(a + b + c\)[/tex] is 56.

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