Common denominators and keep-change-flip are where careless points go to die. The calculator does exact fraction arithmetic — most students just never ask it to.
The move: Let the calculator do exact arithmetic.
Why it works: Desmos computes exactly and can display results as fractions, so “(3/4) ÷ (2/5)” is typing, not technique — and “20% of 80” is just 0.20 × 80.
The pattern
- Rewrite the words as a calculation
- Type it exactly
- Read the exact result
Worked example: What is 3/8 + 5/12?
- Type the sum as fractions.
(3/8)+(5/12) - Desmos shows 0.791666… — tap the fraction icon beside the result to see it EXACT: 19/24.
- Common denominators are now the calculator's problem, not yours.
Worked example 2: What is 15% of 240?
- “15% of” means “0.15 times.”
0.15 · 240 - 36. Every percent question is a decimal multiplication in disguise.
Remember it on test day
Percent = times a decimal. That's the whole cue — say it when you see this question type and the steps follow.
When this isn't the move
Fraction concept questions (comparing sizes, number-line placement) reward estimation sense — don't reach for the keypad first.
Drill it until it's reflex
This move is one of Desvantage's 18 training modules: a plain-English lesson, a type-it-yourself walkthrough inside a live Desmos calculator, and a 100-question drill bank that deals ten fresh questions per round. The first two modules — plus the 12-question diagnostic — are free.