Direction: what should come in place at question mark(?).

$$ {4\over 7}×{2{4\over 5}÷{2\over 5}=?}$$

The sum of the squares of 2 number is 146 and the square root of one of them is 5. The cube of the other number is 

By what least number should 4320 be multiplied so as to obtain a number which is perfect cube? 

Simplify : $$ {(2x)^{2}-(2y)^{2}-(4x)^{2}}$$

Direction: What approximate value will come in place of the question mark (?) in the following question? (You are not expected to calculate the exact value)

(31.99)^1/5 × (80.78)^1/4 × (5.15)² = ? × 2.29

$$ \sqrt{0.00004761} $$   equal to

If $$ {0.7\over 1-6c}=-0.2$$ then what is the value of c.

The largest number of five digits, which is a perfect square is