How do you divide 29/17 mentally without pen and paper?

Hi there,

One option is long division!

17 goes into 29 once, with 13 remaining. 17 goes into 130, 7 times with 11 remaining. 17 goes into 110, 6 times.

Therefore, 1.706.

Mentally

 30/15 = 2. Since 29 (numerator) is lower AND 17 (denominator) is higher, we know this must be less than 2. 

30/20 is 1.5.

Therefore, we pick around 1.7/1.8 (in between the two)

Hi there,

I think this is an interesting question that may be relevant for many people. I would be happy to share my thoughts on it:

• First of all, you can run this calculation precisely (i.e., proper mental math) or roughly, if sufficient (i.e., meaningful roundings).
• If you need to do it precisely, obviously, you would need to run through all calculations, i.e., 29 / 17 = 1 with 12 remaining, 120 / 17 = 7 with 1 remaining, 10 / 17 = 0 with 10 remaining, and so on.
• If you may provide an estimate, you could round to 30 / 15 = 2. Given both the numerator was rounded up and the denominator was rounded down, the actual result needs to be slightly lower.
• Lastly, while this might be a calculation that you are expected to perform mentally, it is absolutely fine to perform most calculations in writing.

If you would like a more detailed discussion on how to best prepare for your upcoming interviews, please don't hesitate to contact me directly.

Best,

Hagen

Hi Joël,

Q: How do you divide 29/17 mentally without pen and paper?

I would start by asking if you can approximate.

1. If you can :
   1. Simplify as 30/15= 2
   2. Since the denominator is higher and the numerator lower, explain the real final number should be a bit lower
2. If you cannot, you will have to do the actual division:
   1. Recognize that 29/17 = 1 with a remainder
   2. Remainder: 29-17=12
   3. Recognize that 120/17 = 7 with a remainder
   4. Result is 1.7 with a remainder
   5. Most of the time this will be enough, if not, you can continue

Please keep in mind that unless they explicitly ask to do the math in your head you will be able to use pen and paper.

Best,

Francesco

Hi there, 

I'd round the numbers: 30 / 15 = ~2

But why can't you use pen and paper in the first place? You're totally allowed to do that during consulting interviews. They're not testing whether you're some mathematical mastermind :) In fact, the recruitment process emphasises more communicational and relational skills. 

Best,
Cristian

Hi there,

Some good answers already. Long division is the way to go for precision, which is doable w/o paper. Otherwise, approximating by rounding numerator/denominator is the way to go.

What I would advise for either option is the following: don't ask if you can do it this way or whether you should do it that way. This is not an exam, you're not a student, and the interviewer is not your teacher.

This conversation is meant to be eye-to-eye. Hence, my advice is to confidently establish yourself what precision is needed and tell them how you're going to do it. They can still intervene but most likely won't.

Hope this helps a bit. Best of luck!

Moritz

You have to be used to playing with numbers. There's no “trick”, only practice.

29/ 17 → 1 + 12/17 → 1 + 12/18 →  1 + ⅔ →  1.67 
(round up because 12/18 < 12/17) → 1.7