The ratio of water to cement is 20:30 meaning that for every 20 parts of water, we have 30 parts of cement. There are 20+30 = 50 parts total.
Divide the number of parts of water (20) over the total number of parts (50) 20/50 = 2/5 = 0.40 use a calculator or long division to find the decimal form of 2/5 to be 0.40
Then move the decimal point 2 spots to the right to go from 0.40 to 40%
Non zero digits are always significant. any zeros between two significant digits are significant. a final zero or trailing zero in the decimal portion only are significant.
