How do you multiply #0.31*69#?

2 Answers
Mar 24, 2016

#0.31 * 69 = 21.39#

Explanation:

If you are calculating it in your head, you might be best off doubling #69# five times, subtracting #69#, then dividing by #100#, since #2^5=32#

#69 -> 138 -> 276 -> 552 -> 1104 -> 2208 -> 2139 -> 21.39#

Mar 24, 2016

There will be different approaches. All as effective as each other. Here is another one

21.39

Explanation:

#0.31" is "31/(color(magenta)(100)#

Consider #x xx31 =( x xx3xx10) +x#

So #[color(white)(.)(69xx3xx10) +69color(white)(.)]color(magenta)(-:100) =2139/100 = 21.39#