Write your own question, step by step
“A shop's coins are 1c, 4c and 6c.
Write a sum-and-difference question of your own about them, and give its answer.
This one has more than one right answer
- This question does not want an answer — it wants a QUESTION, and one you make up yourself. So the first thing to settle is what would make yours a good one, and there is only one requirement: it has to have the answer you were given.
- The question you write must have the exact answer named in the prompt.
- Working backwards is the whole method. Pick something, work out what its answer would be, and keep it if that is the answer you were asked for. 9 and 11 works, for instance — but it is not the answer, it is AN answer.
- Now check every possible choice. The pairs adding to 20 are 9 and 11; 8 and 12; 7 and 13; 6 and 14; 5 and 15; 4 and 16; 3 and 17 and 2 and 18 — 8 in all.
- So 8 different questions would all have been right, and yours matching nobody else's is not a mistake. Working out how many ways there are is its own piece of mathematics, and it is the one this question was really asking.
How it works.
- 01
This question does not want an answer — it wants a QUESTION, and one you make up yourself. So the first thing to settle is what would make yours a good one, and there is only one requirement: it has to have the answer you were given.
- 02
The question you write must have the exact answer named in the prompt.
- 03
Working backwards is the whole method. Pick something, work out what its answer would be, and keep it if that is the answer you were asked for. 9 and 11 works, for instance — but it is not the answer, it is AN answer.
- 04
Now check every possible choice. The pairs adding to 20 are 9 and 11; 8 and 12; 7 and 13; 6 and 14; 5 and 15; 4 and 16; 3 and 17 and 2 and 18 — 8 in all.
- 05
So 8 different questions would all have been right, and yours matching nobody else's is not a mistake. Working out how many ways there are is its own piece of mathematics, and it is the one this question was really asking.