Guest Posted August 6, 2008 Report Share Posted August 6, 2008 heres another variation on the think of a number trick: bob: hey jen! think of a number! jen: okay, got it bob: now add 2 and multiply by 5 jen: yup bob: add 15 and then multiply by 2 jen: got it bob: so whats your number? jen: 180 bob: was your original number 13? jen: yeah! so what was bobs method to figure out jens original number? the answer jen gave bob ended in zero [this works with any other number] so all bob had to do was knock off the zero and subtract 5. heres the math: number =m add 2 =m+2 times 5 =5(m+2) =5m+10 add 15 =5m+10+15 =5m+25 times 2 =2(5m+25) =10m+50 heres what goes on in your head: divide by 10 =m+5 subtract 5 =m :] Quote Link to comment Share on other sites More sharing options...
0 Guest Posted August 7, 2008 Report Share Posted August 7, 2008 heres another variation on the think of a number trick: bob: hey jen! think of a number! jen: okay, got it bob: now add 2 and multiply by 5 jen: yup bob: add 15 and then multiply by 2 jen: got it bob: so whats your number? jen: 180 bob: was your original number 13? jen: yeah! so what was bobs method to figure out jens original number? the answer jen gave bob ended in zero [this works with any other number] so all bob had to do was knock off the zero and subtract 5. heres the math: number =m add 2 =m+2 times 5 =5(m+2) =5m+10 add 15 =5m+10+15 =5m+25 times 2 =2(5m+25) =10m+50 heres what goes on in your head: divide by 10 =m+5 subtract 5 =m :] thats cool and it actually works! Quote Link to comment Share on other sites More sharing options...
0 Guest Posted August 7, 2008 Report Share Posted August 7, 2008 cant u just do the problem backwards? Quote Link to comment Share on other sites More sharing options...
0 Gambit Posted August 7, 2008 Report Share Posted August 7, 2008 cant u just do the problem backwards? yeah thats what I was thinkin' Quote Link to comment Share on other sites More sharing options...
0 Guest Posted August 13, 2008 Report Share Posted August 13, 2008 cant u just do the problem backwards? You could, but it's not much of a trick if you have to work backwards. It takes too long. Giving a quick answer is more impressive. Quote Link to comment Share on other sites More sharing options...
Question
Guest
heres another variation on the think of a number trick:
bob: hey jen! think of a number!
jen: okay, got it
bob: now add 2 and multiply by 5
jen: yup
bob: add 15 and then multiply by 2
jen: got it
bob: so whats your number?
jen: 180
bob: was your original number 13?
jen: yeah!
so what was bobs method to figure out jens original number?
Link to comment
Share on other sites
4 answers to this question
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.