Three more than twice a number is 19. What is the number?
Hints
Take them one at a time. The first gives nothing away.
1A nudge
Undo the last step first.
2The strategy
The number was doubled and then 3 was added. To go backwards, take the 3 off first and then halve - the reverse operations in the reverse order.
3The full solution
19 - 3 = 16, and 16 divided by 2 = 8. Check: twice 8 is 16, plus 3 is 19.
Solution— no shortcut on this one
Write what happened: the number was doubled, then 3 was added, giving 19. Undo in reverse: 19 - 3 = 16, then 16 divided by 2 = 8. Check forwards: 2 x 8 + 3 = 19. The transferable idea: reverse both the operations and their order, and always check by running it forwards again.
Why this is on the test: Three more than twice a number puts the operations in the opposite order to the words, which is where the translation goes wrong.