UK - Math Olympiad Question | You should be able to solve this without calculators!!

Maths Olympiads are held all around the world to recognise students who excel in maths. The test is offered at many grade levels and provides them with numerous possibilities to win certifications, awards, and even scholarships for higher studies.

[flavrt]

I can’t imagine a more difficult and error-prone solution. How about (8x12)(11x9)x10. I can do this in my head. 96x99=9600-96=9504. Times 10=95040.

[votevote]

For this calculation I will multiple them In a paper normally💖♥

[TheBrainfsck]

What's the logic behind this? The more complicated, the easier it is?!

[merrylbutcher]

12x9=108
108 x 8 = 864
(800 +64)x11 = 8800+704 = 9504
9504x10=95040
Knowing the neat method for a quick multiplication by 11 means it makes sense to keep that as the second last step, then add a zero for the x 10.
Quicker than the algebraic method.

[imonkalyanbarua]

I could do it mentally but I can understand the method which would be useful in bigger numbers.

[pakamvenkateswarlu]

Worst method
Multiply 9*11= 99 and 8*12=96
Multiply 99 and 96 using Vedic method
9504
Multiply this with ten
Orally it can be done

[josejuliopl]

It's faster to do the multipications directly

[Psykolord]

Before watching:

I just outright multiplied them out, tbh.

12x11 = 132, 12x11x10 = 1320, 12x11x10x9 = (1320)x9 = 11880, 12x11x10x9x8 = (11880)x8 = 95040.

After watching:

The trick shown in the video is very useful for those who aren't very confident in their ability to multiply large numbers together. Definitely worth trying out!

[MillaSemina]

Omg my kid can do it in her head. I asked her on the way to gymnastics. She said 96x10 is 960 and 960×99 is 96000-960, so 95040

[wfukfm]

Maybe good practice for algebra but just to get the answer group each pair and add a zero for the times 10 : i.e. 72 x 132 add a zero, 95040

[DrAndyShick]

Not only did I not need a calculator, I did this in my head in less than 15 seconds. 9x11=99. x10=990. Multiply that by 96. I turned this into

[bowlchamps]

The trick here is to identify that 9x99 is a very easy number to multiply with. 8x12 is even simplier and x10 the simplest of all.

[yvessioui]

Inefficient... at least there is a moore efficient way. First, group the terms by the easiest way to calculate the last step : 10x(9x11)x(8x12)... because by 11 is easy to find and implies repetition in the part answer --> 10x99x96 --> 10x9504 ---> 95040. That way there is less chance for mistakes and only one real operation to be done by hand the long way (99x96).

[dileepmv]

isnt it easy to multiply them? I was thinking you will be using (x+y)(x-y)

[votevote]

For this takes too much times so I calculate normally it's too easy than this இதுக்கு பருத்தி மூட்டு குடோன்லே இருகலாம் 💐👌💖♥

[secondfirstsecond]

Thats very impressive, next challenge is 1 x 1 = ?, No calculator please.

[GhajabiramSriramulu]

This solution might help for bigger numbers

[nenemtiaof]

Multiplicar direto é muito mais simples.

[jowbloe]

This doesn't seem very hard.
8 x 9 = *72* x 10 = *720* x 11 = 7200 + 720 = *7920*
7920 x 12 is the first point I have to actually think a little bit. Don't even need to write anything down.

[jacholgoogle]

There are a number of permutations of working this out, all much easier and quicker than this 14 step process.