What I discovered using the 2005 edition of “Cracking the GMAT” (The Princeton Review) was that algebra problems can be solved without using algebra, but an easier method: plugging in.
Basically you just replace with number the unknown data represented with letters. Sounds stupid, but it works and you gain time.
Plugging in a number in the question:
- Pick one or more numbers to replace the letters in the problem (question)
- Using your numbers, find an answer to the problem
- Plug your numbers into the answer choices to see which choice equals the answer you found in step 2
Plugging in a number in the answers:
- Always start with answer C. Plug that number into the problem and check if it gives you a solution.
- If choice C is too small, choose the next larger number
- If choice C is too big choose the next smaller number
If the question contains “must be”, “could be” or “cannot be”, the problems can be solved by plugging in but you may need to plug more than one number.
You must have at least as many distinct equations as you have variables for the equation to be solvable.
ax² + bx + c = 0
x = [-b +/- √ (b²-4ac)] / 2a
Also, simultaneous equation can be solved an addition or subtraction of one equation from the other. This way you can eliminate one of the unknowns.
GMAT’ “most wanted”:
- (x + y) ² = x² + 2xy + y²
- (x + y)(x – y) = x² – y²
