how to solve this question.. any input

the informant · Guest

2^20 * 2^19 =

and what is the answer for the units digit

beatthegmat · Posted: Sat Oct 27, 2007 2:22 pm Post subject:

Moved to PS forum area...

me4mba · Posted: Sat Oct 27, 2007 3:54 pm Post subject:

The question asks for the unit digit only?

2^20 * 2^19 = 2^(20+19) = 2^39

The trick is to recognize the pattern of 2^x

2^1 = 2
2^2 = 4
2^3 = 8
2^4 = 16
2^5 = 32
2^6 = 64
2^7 = 128 ...

You can see that the unit digit of 2^x repeats every 4 increments of x.

From that, we know that 2^40 must have a unit digit of 6 and 2^39 will therefore have a unit digit of 8.

qell · Guest

how do you solve

2^20 - 2^19

ri2007 · Posted: Sat Oct 27, 2007 6:15 pm Post subject:

have solved this earlier - check this link

http://www.beatthegmat.com/viewtopic.php?t=6325