# Finding the Percent of a Number

#### Middle and Upper Level

**ISEE Quantitative Comparison:**

**Column A**

40% of 80

**Column B**

90% of 30

**Solution:** There are a few ways to find the percent of a number, so you can choose the one that’s easiest and fastest for you.

__The Decimal Method__

Convert your percentage into a decimal by moving the decimal point two places to the left. Then, multiply the number by that decimal.**Column A:** 40% = 0.4 → 0.4 x 80 = **32****Column B:** 90% = 0.9 → 0.9 x 30 = **27**

**Helpful Tip:** Estimate the percentage using a close fraction to make sure your answer is reasonable and ensure against decimal point errors. 40% is a little less than 50% (half), so column A should be a little less than half of 80. 90% is a little less than 100% (one whole), so your answer should be a little less than 30.

__The Ratio Method__

Convert your percentage into a ratio over 100, and then multiply the ratio by the number. Reduce and cross-cancel to make the math easier.

**Helpful Tip:** The ratio method works best for ratios that are easily reduced to simple fractions and numbers that can cross-cancel with those fractions.

**Column A:**

**Column B:**

__The 10% Shortcut__

STEP 1: Find 10% of your number by moving the decimal point to the left once. If your number ends in 0, remove the zero. **Column A:** 10% of 80 = 8 **Column B:** 10% of 30 = 3

STEP 2: Divide your percent by 10. **Column A:** 40% ÷ 10 = 4 **Column B:** 90% ÷ 10 = 9

STEP 3: Multiply your 10% value by the percent’s multiple of 10. **Column A:** 8 × 4 = 32 **Column B:** 9 × 3 = 27

**Helpful tip:** Use the 10% shortcut to mentally calculate percentages that are multiples of 10 (30%, 70%, etc). You can also use it with multiples of 5, as 5% is half of 10%.

No matter which method you use, column A is greater.