Step 1: Proof of a Will.
To prove a Will, it must be shown that it was duly executed by the testator and represents his last testamentary intention.
Step 2: Mental capacity.
The Will must satisfy the test of a prudent and sound disposing mind of the testator at the time of execution.
Step 3: Irrelevant requirement.
There is no legal requirement that a Will must satisfy any test of mathematical accuracy.
Step 4: Conclusion.
Hence, the correct answer is (D).