book Maths Puzzle Numerical Ability

solving for x:
3n-2/5 = 7/10

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book Other Question

general term of infinite sequence: tn= pie(3/11)^(n+1) , pie=3.14....
How many terms must be added to reach a sum that is greater than 0.32?

i know at least 5 terms are needed x=1,y=-2
3x^2y-4xy^2+xy