Question

Manuel bought 6 postcards during 3 days of vacation. How many days will Manuel have to spend on vacation before he will have bought a total of 20 postcards?

Answer 1

10 days

Explanation:

The problem seems to assume that Manuel will continue to buy postcards at exactly the rate of 2 per day during his whole vacation. 2×10 = 20, so it will take 10 days to accumulate 20 postcards.

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If you like proportions, you could write one:

days/postcards = 3/6 = ??/20

Multiplying by 20 gives ...

20(3/6) = ?? = 10 . . . . . 10 days on vacation will result in 20 postcards