ah, basically what length can you divide each string to get a certain length
factor each
8=2*2*2
therefor:
8=1*8=2*4=4*2=8*1
so you can have 1 length of string 8cm long
2 lengths of string 4cm long
4 lengths of string 2cm long
8 lengths of string 1cm long
20cm string
factor
20=1*2*2*5
so 20=1*20=2*10=4*5=5*4=10*2=20*1
you can have 1 string 20cm long
2 strings 10cm long
4 strings 5cm long
5 strings 4cm long
10 strings 2cm long
20 strings 1cm long
we need greatest common length
in 8cm stirng, we have 1,2,4,8
in 20cm string, we have 1,2,4,5,10,20
greatest common length is 4
answer is 4cm
alternately, you could have done this:
8=2*2*2
20=2*2*5
common grooup is 2*2=4 so 4 is answer
