Nobody calculates so many lines.In chess,you've "Candidate Moves".you have to calculate a bit and choose your move from those Candidate moves.
In every system,there is already tons of theory got developed and in middle game and endgame,there are specific theories to follow.Its not that hard when someone teaches you.But of course,it is not that easy.Like a basic mate pattern-Bishop and Knight mate attack.Even Grandmasters fail to deliver it on board.
By the way,this is a good article on the event...
Future stars at the World Youth | chess24.com
and this is another one......
Indians sweep 11 medals in World Youth Chess Championships
Diwali celebrations came early for young Indian chess players as they won as many as 11 medals, including five gold, three silver and three bronze at the World Youth Chess Championships at Porto Carras in Greece. M Mahalakshmi (Girls Under-18), R Vaishali (Girls U-14), her younger brother R Pragnanandaa (Open U-10), Rakshita Ravi (Girls U-10) and Bharath Subramaniyam (open U-8) dominated their respective sections to win the gold medal while Nihal Sarin (Open U-12) missed it by a whisker to settle for silver.
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Dev Shah (Open U-8) and V Varshini (Girls U-18) were the other two silver medallists. The bronze medals were bagged by Vantika Agrawal (Girls U-14), Saina Salonika (Girls U-12) and Divya Deshmukh (Girls U-10). The World Youth Chess Championships is amongst the biggest event in the world with participation of players from across the globe. India had fielded a total of 50 players in 12 categories held in under-8, 10, 12, 14, 16 and 18 age group separately for girls and the other section is called the open group.
India’s performance as a team was the best by a huge margin as other competing countries, at best, got one gold medal each. Russia and United States got four medals each but none of them was a gold. The Indians had won five gold medals in the 2006 edition also when the event was held at Batumi in Georgia. However, back then, Russia, one of the biggest powerhouse in chess, had not participated.
Out of the five gold medalists, three had tasted similar successes before. Mahalakshmi had won the world title in Under-14 category in 2012, Vaishali won the under-10 in 2012 and Praggnanandhaa had won the Under-8 section in 2013. For Bharath and Rakshitta it was their maiden world title. Interestingly, all the five gold medal winners are from a single academy in Chennai called the Chess Gurukul headed by Grandmaster R B Ramesh.
Indians sweep 11 medals in World Youth Chess Championships | Latest News & Gossip on Popular Trends at India.com