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In a colony, 60% of the houses have a water tank on the roof. What is the ratio of houses WITH a tank to houses WITHOUT one?

Class 7Comparing QuantitiesComparing Quantities
  • A3 : 2
  • B2 : 3
  • C3 : 5
  • D60 : 100

Step-by-Step Solution

If 60% have a tank, then 100% − 60% = 40% do not. The ratio with : without = 60 : 40, and dividing both terms by 20 gives 3 : 2. The trap in 3 : 5 is comparing the 60% with the WHOLE colony instead of with the houses that have no tank — that would be the fraction, not this ratio. 2 : 3 is the ratio reversed, and 60 : 100 is neither the right comparison nor in simplest form.
Answer: A) 3 : 2

Key idea: Reading the question carefully

Three things to check before you compute:

1. **What's being asked?** Profit % needs CP and SP. SI needs P, R, T.
2. **What units are the inputs in?** Time in months → convert to years (divide by 12). Rate already per annum → leave it.
3. **What's the base of the percentage?** Profit/loss % is on COST price, not selling price. Discount % is on MARKED price, not on what you actually paid.

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