300 Foul Shots

Date: 07/11/2001 at 21:13:36
From: Roger Waters
Subject: Unknown formula

A basketball player shoots 100 foul shots on a given day, and 
increases the number he shoots by 10 per day.

Number of days	Number of shots taken
       1               100
       2               110
       3               120
       4               130
       5               140
       6               150

After how many days would the person have shot 300 foul shots?

I know the answer is 21, but I need the formula. Thanks

- Andrew

Date: 07/11/2001 at 21:47:32
From: Doctor Jaffee
Subject: Re: Unknown formula

Hi Andrew,

Look at it this way:

Number of days     Number of shots taken
    1                100 = 100 + 0(10)
    2                110 = 100 + 1(10) 
    3                120 = 100 + 2(10)
    4                130 = 100 + 3(10)
    5                140 = 100 + 4(10)
    6                150 = 100 + 5(10)
    .
    .
    .
    n                   300 =  ?

Notice the pattern that I have established. In particular, notice the 
number being multiplied by 10 in each row compared to the number of 
the day. You should be able to figure out the formula now.

Give it a try and if you want to check your solution with me, write 
back. If you are having difficulties, let me know and show me what you 
have done so far, and I'll try to help you some more.

Good luck.

- Doctor Jaffee, The Math Forum
  http://mathforum.org/dr.math/