Firefighter Steve was born in 1950. Steve had a grandmother who was born in a year which is the product of two prime numbers, one of which is one less than twice the other. In what year did Steve’s grandmother celebrate her 90th birthday?
Steve's Grandmother was born in the year 1891. 1891 =61 x 31 and 31*2 - 61 =1.
So, Steve's Grandmother celebrated her 90th birthday in: 1891 + 90 =1981.
