In an exam, 3 marks are scored on the correct solution, but 2 marks are deducted on the wrong solution. If a student scores 75 questions and gets 75 marks, the correct answer is the number of questions.

What is the L.C. M of  $$ {2\over 5},{3\over 10},{4\over 15}$$.

The L.C.M and H.C.F of the two numbers are 84 and 21 respectively. If the numbers have a ratio of 1: 4, what is the larger number?

If 1.5a=0.04 b then find out the value of $$ {b-a\over b+a}$$.

If $$ {9^{x}={9\over {3^{x}}}}$$ then find the value of x.

If $$ {(x^{3})^{3} × x^{5}\over{x^{4}}}=x^{n}$$ then find the value of n.

What should be added at least in 1140 so that it becomes a perfect square?

$$ {\sqrt{8\ {^{3}\sqrt{729}}}=?}$$