Hands-on math!

Washington State Math Olympiad
Hints and Solutions
2008 Grade 7 Algebra

Problem
Solution
1) There is a population of 832 rabbits in the city of Lakewood. The population of rabbits doubled every six months. What was the population of rabbits 30 months ago? 30 months ago is ____ doubling cycles
There are 2 ways to solve this problem:
  1. Method 1: Brute force! Use your calculator to successively divide 832 by 2 5 times = _______ rabbits
  2. Method 2: Use powers of 2:
        Let P = the rabbit population 30 months ago.
    Write the equation for P and solve:


    P = ______ rabbits.
2) What is the next term in this sequence:
    1, 2, 2, 4, 8, 32, 256, __ ?

  1. You must find what each term is using previous terms.


  2. The next term is _______
3) Study the sequence of shapes below built out of squares. How many squares would be in the 10th term of the sequence?
Let n = the term number (1, 2, 3, ...)
  1. The top row is _____
  2. The bottom vertical squares are ____
  3. The ones in between are ________
  4. So add these up to get the total number of squares in the nth term is:


    ___________________
  5. So, using this expression, the 10th term is ___________

Problem
Solution
4) A ladybug is walking along the bottom edge of a window frame. The y-axis shows distance from the corner of the window frame in inches. The x-axis shows time in seconds. How fast is she walking? The speed of the ladybug is the slope of the line.

The ladybug's rate = _____ inch/second
5) The flat bottomed rectangular pool is being drained. The water level is given by

    water level at time t minutes = 6 - 0.05t feet

How long will it take for the water level to drop to 3 feet?
Express your answer in hours and minutes.
Let L = the water level
L = 6 - 0.05 t
Solve for t = _____________