A certain number N divided by one more than itself yields one fifth.

Another number M divided by one more than itself yields one fifth of itself.

It is quite easy to find the product M*N.

**Try to do it " by heart" i.e. no calc, no pen, no paper.**

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(In reply to

I think I've got it ..... by K Sengupta)

KS,

"By heart" solution is obtained as follows:

M+1=5 ==> **M=4 from your (ii)**

5*N=N+1 ==> **N= 1/4** **from your (i) **

**......................................**

**ERGO: MN=1**