how to solve this question.. any input

[beatthegmat]

Moved to PS forum area...

[me4mba]

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.

[ri2007]

have solved this earlier - check this link

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