# Algebra

**Problem**

In still water, your small boat averages 8 miles per hour. It takes you the same amount of time to travel 15 miles downstream, with the current, as 9 miles upstream, against the current. What is the rate of water's current?

A. 4 miles/hr | C. 2 miles/hr |

B. 3 miles/hr | D. 5 miles/hr |

**Problem**

Given the following equations:

$$ab = 1/8 \qquad ac = 3 \qquad bc = 6$$

Find the value of $a + b + c$.

A. $12$ | C. $\dfrac{4}{51}$ |

B. $\dfrac{7}{16}$ | D. $12.75$ |

**Problem**

How many terms from the progression 3, 5, 7, 9, ... must be taken in order that their sum will be 2600?

A. 80 | C. 50 |

B. 60 | D. 70 |

**Problem**

Earth is approximately 93,000,000.00 miles from the sun, and the Jupiter is approximately 484,000,900.00 miles from the sun. How long would it take a spaceship traveling at 7,500.00 mph to fly from Earth to Jupiter?

A. 9.0 years | C. 6.0 years |

B. 5.0 years | D. 3.0 years |

**Problem**

A salesperson earns \$600 per month plus a commission of 20% of sales. Find the minimum amount of sales needed to receive a total income of at least \$1500 per month.

A. \$1500 | C. \$4500 |

B. \$3500 | D. \$2500 |

**Problem**

A salesperson earns P60,000 per month plus a commission of 20% of sales. Find the minimum amount of sales needed to receive a total income of at least P150,000 per month.

A. P150,000 | C. P450,000 |

B. P350,000 | D. P250,000 |

## Relationship Between Arithmetic Mean, Harmonic Mean, and Geometric Mean of Two Numbers

For two numbers *x* and *y*, let *x*, *a*, *y* be a sequence of three numbers. If *x*, *a*, *y* is an arithmetic progression then '*a*' is called *arithmetic mean*. If *x*, *a*, *y* is a geometric progression then '*a*' is called *geometric mean*. If *x*, *a*, *y* form a harmonic progression then '*a*' is called *harmonic mean*.

Let *AM* = arithmetic mean, *GM* = geometric mean, and *HM* = harmonic mean. The relationship between the three is given by the formula

Below is the derivation of this relationship.

## Derivation of Sum of Finite and Infinite Geometric Progression

**Geometric Progression, GP**

Geometric progression (also known as geometric sequence) is a sequence of numbers where the ratio of any two adjacent terms is constant. The constant ratio is called the common ratio, *r* of geometric progression. Each term therefore in geometric progression is found by multiplying the previous one by *r*.

**Eaxamples of GP:**

- 3, 6, 12, 24, … is a geometric progression with
*r*= 2 - 10, -5, 2.5, -1.25, … is a geometric progression with
*r*= -1/2

## Derivation of Sum of Arithmetic Progression

**Arithmetic Progression, AP**

Definition

*d*.

Examples of arithmetic progression are:

- 2, 5, 8, 11,... common difference = 3
- 23, 19, 15, 11,... common difference = -4