Worked Example 1
If 12 exercise books cost Rs 540, what would 7 books cost?
Direct or inverse?Fewer books, less money, so direct
Step down to one1 book: 540 ÷ 12 = Rs 45
Step up to seven7 books: 7 × 45 = Rs 315
Sense check315 is less than 540, as it should be.
Worked Example 2
A tank is filled by 8 taps in 6 hours. How long would 12 taps take?
Direct or inverse?More taps, less time, so inverse
Step down to one tap1 tap: 8 × 6 = 48 hours
Step up to twelve taps12 taps: 48 ÷ 12 = 4 hours
Sense checkMore taps, fewer hours. An answer of 9 hours would have meant reversed steps.
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