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### Question

For what value of x would this expression be a perfect square: $6.16 × 6.16 - x × 6.16 + 0.3 × 0.3$?

**A**

0.6.

**B**

0.06.

**C**

0.0006.

**D**

6.0.

**Soln.**

**Ans: a**

Comparing the given expression with $a^2 - 2 × a ×b + b^2 = (a - b)^2$, we see that if a = 6.16, and b = 0.3 then by inspection, x should be equal to 2b = 2 × 0.3 = 0.6.