The Student Room Group

Explain old trick

Write down your shoe size, to the nearest whole number.

Add 50

multiply by 20

add 1000

add 21

take away your birth year

the first 2 digits are your shoe size, the last 2 are your age.
Original post by NJA
Write down your shoe size, to the nearest whole number.

Add 50

multiply by 20

add 1000

add 21

take away your birth year

the first 2 digits are your shoe size, the last 2 are your age.

It doesn't work.
Reply 2
Original post by old_engineer
It doesn't work.

Prove that assertion
Original post by NJA
Prove that assertion

OK let's try shoe size 11 and birth 1991 year (age 30).

Step 1: 11
Step 2: 11 + 50 = 61
Step 3: 61 x 20 = 1,220
Step 4: 1,220 + 1,000 = 2,200
Step 5: 2,200 + 21 = 2,241
Step 6: 2,241 - 1991 = 250
Original post by old_engineer
OK let's try shoe size 11 and birth 1991 year (age 30).

Step 1: 11
Step 2: 11 + 50 = 61
Step 3: 61 x 20 = 1,220
Step 4: 1,220 + 1,000 = 2,200
Step 5: 2,200 + 21 = 2,241
Step 6: 2,241 - 1991 = 250

I'd always assumed you were well into your sixties, with that pfp of a slide rule.
Original post by Reality Check
I'd always assumed you were well into your sixties, with that pfp of a slide rule.

I didn't say that was my age (or my shoe size). :-)
Write down your shoe size, to the nearest whole number. 11

Add 50 61

multiply by 20 1220

add 1000 2220

add 21 2241

take away your birth year 242

the first 2 digits are your shoe size, the last 2 are your age. 24 and 42


My size is 11 and my age is 22 :_: (off by basically a factor of 2)
(edited 2 years ago)
You’ve missed the first step out.
(edited 2 years ago)
Original post by old_engineer
OK let's try shoe size 11 and birth 1991 year (age 30).

Step 1: 11
Step 2: 11 + 50 = 61
Step 3: 61 x 20 = 1,220
Step 4: 1,220 + 1,000 = 2,200
Step 5: 2,200 + 21 = 2,241
Step 6: 2,241 - 1991 = 250


:console:
Original post by GabiAbi84
You’ve missed the first step out.


In which case I'd propose a first step of "multiply shoe size by 5"
Original post by ghostwalker
In which case I'd propose a first step of "multiply shoe size by 5"


That’s the very first step that’s supposed to be there :smile:

(I used to do this to people when I was a kid so I remember the steps- and the logic)
(edited 2 years ago)
Original post by old_engineer
I didn't say that was my age (or my shoe size). :-)


:laugh: good point.
Original post by NJA
Write down your shoe size, to the nearest whole number.

Add 50

multiply by 20

add 1000

add 21

take away your birth year

the first 2 digits are your shoe size, the last 2 are your age.

Your thread title asks 'Explain old trick'. Try substituting letters to represent 'shoe size' and 'age', and see where it leads :smile:
Reply 13
Original post by ghostwalker
In which case I'd propose a first step of "multiply shoe size by 5"

YES!
sorry, I missed that out

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