How do you multiply minutes and seconds by a number eg 3min 45secs x 3?

Answer 1

I can do it in many ways:

• Multiply the minutes and seconds separately, then correct for 60 secs = 1 min

3 mins 45 secs x 3 = 9 mins 135 secs

but 60 secs = 1 min, so 135 secs = 2 mins 15 secs

So 9 mins 135 secs = 9 mins 2 mins 15 secs = 11 mins 15 secs.

⇒ 3 mins 45 secs x 3 = 11 mins 15 secs

• Work in seconds and convert back at the end

3 mins 45 secs x 3 = 225 secs x 3

= 675 secs

= 11 mins 15 secs

• Convert the seconds to a decimal of a minute, work it out and convert back at the end

3 mins 45 secs x 3 = 3.75 mins x 3

= 11.25 mins

= 11 mins 15 secs

• I am actually more likely to work with fractions as opposed to decimals as decimals can lead to inaccuracies

3 mins 45 secs x 3 = 33/4 mins x 3

= 15/4 mins x 3

= 45/4 mins

= 111/4 mins

= 11 mins 15 secs

• Work with the mins and seconds directly using sexagesimal (base 60) numbers

To avoid having to invent 50 new symbols for the numbers 10-59, I use the decimal numbers, but separate the sexagesimal "digits" by colons - like a digital clock.

3 mins 45 secs x 3 = 3:45 x 3

45 x 3 = 15 carry 2

3 x 3 + carry = 9 + 2 = 11

⇒ 3:45 x 3 = 11:15

⇒ 3 mins 45 secs x 3 = 11 mins 15 secs.