ACT Math: Master Mental Math Shortcuts for Speed

Trick 1: Multiply by 5. Instead of 7×5, think 7×10÷2=35. Divide by 2 is faster than multiply by 5. Trick 2: Multiply by 11. For 23×11, think 20×11+3×11=220+33=253. This is faster than long multiplication. Trick 3: Square numbers ending in 5. For 35^2, use (30×40)+25=1200+25=1225. For any number ending in 5, multiply the first digit by the next digit, then append 25. Trick 4: Percent calculations. For 15% of 40, think 10% of 40=4, then add half: 4+2=6. Trick 5: Quick estimation of fractions. 1/3≈0.33, 1/4=0.25, 1/5=0.2. Memorize these conversions. These five tricks shave 1-2 minutes off your Math section because you spend less time on a calculator and more time on strategy.

Example: "What is 15% of 240?" Without a trick, you might calculate 0.15×240 on the calculator, taking 8 seconds. With Trick 4: 10% of 240=24, 5%=12, total=36. Four seconds and no calculator needed.

Trap 1: Using a mental shortcut for a problem where exact calculation is required. If the problem asks for a precise answer, do not estimate; calculate exactly. Trap 2: Relying on a trick you have not practiced enough. If you half-remember a trick and mess up, you waste more time than you save. Only use tricks you know cold. Trap 3: Confusing the trick or using it in the wrong context. Tricks are for specific problem types; do not try to force a trick onto a problem it does not fit. Smart students use mental math tricks strategically, not reflexively; they ask "Is this problem a candidate for a trick?" before attempting one.

On your next practice test, mark every problem where you used a shortcut. If it saved time and was correct, great. If it caused confusion or wrong answer, practice that trick until it feels automatic before using it on test day.

Day 1: Multiply by 5. Solve 10 problems of the form A×5 using the trick (A×10÷2). Day 2: Multiply by 11. Solve 10 problems. Day 3: Square numbers ending in 5. Solve 10 problems. Day 4: Percent calculations. Solve 10 problems. Day 5: Estimate fractions. Solve 10 problems. Time yourself on each set. By Day 5, you should be 50% faster than Day 1 because the tricks are now automatic. This one-week drill burns the five tricks into your brain so that on test day, you use them without thinking, saving 1-2 minutes total and freeing up time for harder problems.

Do this drill once, then revisit the tricks that gave you the most trouble. By test day, all five should feel second nature.

ACT Math has 60 questions in 60 minutes, roughly one minute per question. But some questions take 30 seconds, and some take two minutes. Mental shortcuts let you solve 30-second problems even faster, banking time for the two-minute problems where the actual thinking happens. A student who masters five mental math tricks saves 2-3 minutes per test section, time that translates directly to solving more hard problems and raising her score by 2-3 points.

This week, learn the five tricks. By test day, they will be automatic. You will thank yourself when you are flying through the Math section and your friends are still typing into calculators.