Excel calculation- How do you reference the same cell?

[JEDI]

ie:
A1 = 100

B1 = .05
b2= .1
b3 = .15
...
b19=.95
b20=1

c1= a1* b1
c2=a1*b2
c3= a1 * b3

when i drag the formula down, it changes to:
c2=a2*b2
c3= a3*b3

how do i keep A1 as the cell to use in the calcs?

 

[xtknight]

Use $A$1

Cell references with dollar signs in front of just the number, or in front of just the letter, are called ?Mixed Cell References.? Use a mixed cell reference in a formula when you want to create a set of formulas that will always refer to either one specific row: A$1, or one specific column: $B2. If the formula should always use the same cell reference, add two dollar signs: $C$3. This is called an ?Absolute Cell Reference.?

 

[JEDI]

ah.. thx!

i couldnt remember that. and when i did a search in Excel help for 'Absolute', all i got was absolute numbers.