10y old Terence Tao with 72y old Paul Erdős in 1985 in Adelaide, Australia.
During Paul's visit to Adelaide, he discussed mathematical problems with Tao, recognizing his immense potential and encouraging him to pursue mathematics.
In the 1930s, Paul Erdős posed the problem - if every infinite sequence of +1s and -1s must contain subsequences whose sums are arbitrarily large.
80 years later, in 2015, Terence Tao solved the Erdős discrepancy problem, he proved that Erdős's conjecture was wrong and such a sequence cannot be constructed, as the sums will inevitably grow to be arbitrarily large.