Estimation, Rounding, and Calculator Skills

Section 1Why estimation matters

Estimation is a quick check using rounded numbers. It does not replace exact working, but it helps you judge whether an answer is sensible. If a grocery total near J$5000 comes out as J$50, your estimate should warn you that something is off.

Section 2Decimal places

Decimal places count digits after the decimal point. To round to 2 decimal places, keep two digits after the point and inspect the next digit. If the next digit is 5 or more, round up; if it is less than 5, keep the digit the same.

Section 3Significant figures

Significant figures count from the first non-zero digit. In 0.00482, the first significant digit is 4, not any of the zeros before it. Easy to mix up - 0.00482 to 2 significant figures is 0.0048, not 0.00.

Section 4Zeros and significance

Zeros between non-zero digits are significant, so 1005 has four significant figures. Zeros at the end of a decimal can also be significant, such as 2.50 having three significant figures. Watch out: 2500 is ambiguous unless the question gives a level of accuracy or uses scientific notation.

Section 5Order of operations

Order of operations tells you what to calculate first: brackets, powers and roots, multiplication and division, then addition and subtraction. Multiplication and division are done from left to right, not multiplication always before division. Addition and subtraction are also done from left to right.

Section 6Calculator use

A calculator is powerful, but it only follows what you enter. Use brackets for fractions, negative numbers, and grouped terms. The thing to remember is: if the written expression has a numerator or denominator with more than one term, your calculator entry probably needs brackets.

Section 7Reasonable final answers

Many CSEC-style questions expect final answers to a stated accuracy, such as 3 significant figures or 2 decimal places. Do not round too early in the middle of a calculation unless the question tells you to. Keep extra digits, then round the final answer.