Solve large # multiplication in less than 10 seconds

.MintBerryCrunch

.MintBerryCrunch

Member
So I'm a double major in math and accounting and somehow had never heard of this before today, go figure. You may already know this method but for those of you who don't here is an easy way to make yourself intelligent.

Take 93 and 98 for example. We establish that 100 is a good baseline for both of these numbers. 93 is 7 away from 100 and 98 is 2 away from 100.

This leaves us with two integers -7 and -2. 98-7=91 and 93-2=91. This gives us the first two digits of the solution (91).

Now we multiply these intergers -7*-2=14. This gives us the final two digits of the solution (14)

9114

 
85x75

75-15=60

85-25=60

15+25=40

So 85x75=6040?

Nope, It's 6375

I think I did that correctly by your method.
 
I tried 78 and 77 with 80 as a base.

thats 77 -2=75 ans 78-3= 75

then -2 x-3 = 6

I either get 756 or 7506 but neither is the correct answer, which is 6006

either this dosent always work or I did something wrong.
 
multiply 15*25 gets you 375, add it to 6000. the first 2 last two thing only works if the 2 numbers multiply to double digits. Otherwise assume 60 is short for 6000 and add the second part.
 
just doing it in my head, I think the base always has to be 100. If you do that then you get the correct 6006, and every other base gets you a different answer.
 
I majored in math and actually teach it. This is always a neat trick to play with kids to trick them....or bet money on it.
 
I would love having you as a math teacher... yet absolutely hate it. Teachers who fuck we me every day piss me off
 
cool i'm gonna use this.
but for your's in particular, since 98 is so close to 100 I would do it in my head like this...
93*100= 9300 then (93*2) or 186 so 9300-186= 9114

im gonna try one
67*86
5300 + 14*33.......times 14by 10=140, then times 3 (because 30) = 420 + (14*3) =462
answer: 5762 i think
yaaa your method works very well for some but others you can write it down on paper and do it in 10seconds vs stressing your brain
and as for the calculator comments, ive taken two math courses at university neither of them permitted calculators
 
Easy to get a job

Million different job options

Very useful skill

Payed alot of money

Not a very popular major

 
all very valid points I suppose.

I would still never major in math, just not my cup of tea. I would want to major in something that I like/find interesting, i guess the OP finds math interesting enough to do so.
 
A double math major? Props for posting that on nS... But srsly, it doesnt wprk and i could just use my calculator?
 
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