Lens 08 of 9
The options
Look at the answer choices as data. Test them instead of solving forward.
When the question hands you four candidates, checking is cheaper than deriving. Plug each option into the condition, cheapest first. The options are part of the question: a student who ignores them is solving a harder problem than the one set.
The clues that call for it
- Arithmetic Progressions
'Which of these is a term of the AP?'
Subtract the first term and test divisibility by d for each option.
- Quadratic Equations
Four numeric options and a heavy equation
Don't solve x² − 7x + 12 = 0 from scratch; test x = 3 and x = 4 from the options.
Worked example
For which value is 2ˣ = 32? (4 · 5 · 6 · 7)
- 1
Refuse the forward route
Taking logs is legal but slower than reading the options.
- 2
Reverse-engineer
You already know the powers of 2 by heart.
2⁵ = 32
- 3
Answer
5. When the answer set is handed to you, checking beats solving.
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