Sizu Home › Calculators › Plug In a Formula
Opens on Chapter 2’s example: 2a + 3b with a = 4 and b = 5.
Enter your numbers, then press Work it out.
How it works
Substitution means replacing each letter with its number. Where letters sat side by side (2a means 2 × a), the multiplication sign comes back once the letter is a number, so 2a becomes 2 × 4, never 24. A negative number goes in brackets, so x² at x = −3 is (−3)² = 9. Then the arithmetic runs in the agreed order: brackets, powers, × and ÷ left to right, + and − left to right.
From the book, Chapter 2. 2a + 3b at a = 4, b = 5 is 8 + 15 = 23. Roz’s pay 18h + 25 is $565 for 30 hours and $385 for 20; a 14 by 12 room is 168 square feet ($588 of flooring); 25°C is 77°F; at x = 5, x² is 25 but 2x is 10; three notebooks and two pens cost $9.50; the taxi is $21.50 for 8 miles and $30.50 for 12. Every chapter and its calculator →
Numbers can be typed as 1,450, $38, 0.40, 12%, 1/6 or 2 3/8. The algebra is done with exact fractions, so 1/3 stays 1/3; decimals are rounded half up, the way the book rounds. Everything stays in your browser: no sign-up, nothing stored or sent.