If $$ {x+{1\over x}=7}$$ then $$ {x^{2}+{1\over {x^{2}}}=?}$$

If $$ {\sqrt{2x+9}+x=13}$$ then find the value of x?

A furniture salesman increased the value of furniture by 20 percent due to the lure of more income, which led to a decrease of 30 percent in his sales, then tell him what percentage was reduced in his income?

The weight of a bucket full of water is 36 kg. If the weight of a half-filled bucket is 21 kg, what will be the weight of the empty bucket?

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 $$ {b-a\over b+a}$$.