Alan travels 3/10 of his journey car. 3/20 by bicycle 1/12 by boat and walks the rest what fraction of the journey did he walk? if the journey is 140 km, how many km did he walk?

The denominators are: 10, 20, and 12
The LCD (lowest common denominator) is 60 as this is the smallest multiple of 10, 20, and 12.

Get each fraction to have a denominator of 60
3/10 = (3/10)*(6/6) = (3*6)/(10*6) = 18/60
3/20 = (3/20)*(3/3) = (3*3)/(20*3) = 9/60
1/12 = (1/12)*(5/5) = (1*5)/(12*5) = 5/60

The fractions 
3/10, 3/20, and 1/12
are equivalent to
18/60, 9/60, and 5/60
in that exact order

Add up the second set of fractions to get
(18/60) + (9/60) + (5/60) = (18+9+5)/60 = 32/60 = 8/15

The result of adding the fractions and reducing leads to 8/15 meaning that Alan takes 8/15 of the journey to use his car, bike and boat

The rest of the journey (7/15) is done walking
Multiply this with the total distance 140
(7/15)*140 = (7/15)*(140/1)
(7/15)*140 = (7*140)/(15*1)
(7/15)*140 = (980)/(15)
(7/15)*140 = (975+5)/15
(7/15)*140 = (975/15)+(5/15)
(7/15)*140 = (65)+(1/3)
(7/15)*140 = 65 & 1/3

The answer as a mixed number is 65 & 1/3
The answer as an improper fraction is 980/15
The approximate answer in decimal form is 65.33 (rounded to 2 decimal places)