Kristen Tracey is a Content Developer at Knewton, where she helps students with their SAT preparation.
The SAT lets you use your calculator for any problem, so why would you consider opting out at all? Because a huge part of the test is timing. The faster your mental math is, the faster your test-taking can be.
Below you’ll find a list of six tips for quick calculation. Some are facts you should simply memorize, if you haven’t yet. Our other tricks can help you rack up speed.
Top three memorization tasks:
1. The times tables through 12. Pay special attention to perfect squares and their roots, because they show up everywhere from right triangles to algebra.
2. Cubes of integers up through 5, powers of 3 up through 34, and powers of 2 up through 210 (that’s 1,024). The test-makers love these higher powers, so you’ll have to cozy up to them too!
3. Common fraction-decimal-percent conversions. For example, 25% = .25 = 1/4.
Three speedy math tips:
1. Those times tables can still apply if the numbers end with a zero or zeroes. If you know what 8 × 9 is, you know what 80 × 9 is—just add a zero to the end of the product.
2. Numbers close to a “round” number are easier to add, subtract, and even multiply in your head. For example, 37 × 101 is definitely something you can punch into your calculator, but you might also realize, “Hey! That’s just 37 more than 3700!” That’s because 101 is one more than 100—and 37 × (100 + 1) is the same as (37 × 100) + (37 × 1).
3. Sometimes multiplication can be broken into two simple chunks. Multiplying a number by 4 is the same as doubling the number twice. Multiplying by 5 is the same as multiplying by 10 and then dividing by 2. Multiplying a number by 20 is the same as doubling the number and then multiplying it by 10 (adding a zero). Try applying similar logic with division if you feel comfortable.
But when it comes to decision time—brain or machine?—remember, “can” does not equal “should.”
The very best tip we can give you is not to take risks with either your accuracy or your time. Don’t try to skip the calculator if you think there’s any chance of getting something wrong on your own. As long as you type carefully and mind your order of operations, your calculator won’t let you down.
Likewise, if your typing is faster than your mental math, go electronic. No one’s grading you on whether you use your calculator, so choose the most efficient approach.
In other words, all of our suggestions above should be used only if you’re 100% solid on them—and 110% speedy!
And even if you’re a superstar mental mathlete, the SAT is no time to prove it to yourself. You absolutely should use your calculator for tougher arithmetic, such as long division, arithmetic with exponents or decimals, and even addition of two-digit numbers.
Finally, here’s our inevitable PSA on calculator use: Make sure well before your test date to locate an eligible scientific or (preferably) graphing calculator that you’re familiar with. Before the test, check that your calculator is working, and bring spare batteries (or even a spare calculator). If your calculator malfunctions or runs out of juice, you’re on your own—test centers don’t provide extra equipment, and students can’t share. Sure, the math section is designed so that calculators aren’t strictly necessary, but why find out for yourself?