Here is an easy puzzle:
take a break and solve this puzzle..
a king asks a learned man to visit his palace. the man says i will come any day next month. but give me gold in gms equal to the date on which i come. the king asks the jeweler to make rings of 1 to 31 gms. the jeweler was smart and makes only 5 rings. what was the weights of those rings?

The answer is 
date
1                  2                 3          4             5                                         31
r1                r2               r3           r4          r5               .  .  .                  r31
1gm           2gms         3gms     4gms    5gms        .   .  .                 31gms

r1+r2+ +r31= 31(31+1) /2=496gms  (31 rings)

he only made 5 rings

31 rings> 496 gms
5 rings > ? = 5 x496  / 31=80 gms

 the weights of those 5 rings was 80 gms

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