A natural number, when decreased by 13, equals 140 times its reciprocal. Find the number.
Find a natural number whose square when decreased by 84 is equal to 24 more than thrice the given number.
Twice a number when decreased by 7 gives 45. Find the number.
Find the sum of :
(i) all odd natural numbers less than 50.
(ii) first 12 natural numbers each of which is a multiple of 7.