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.
.

(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

Posted by Ady TZIDON on 2012-01-15 00:58:19