Substituting into a two-letter expression

Difficulty Stretch · Set kgdltn

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1
If x = 12 and y = 11, work out12x−4y=
2
If x = 11 and y = 7, work out5x−4y=
3
If x = 5 and y = 9, work out8x−8y=
4
If x = 12 and y = 7, work out3x−6y=
5
If x = 16 and y = 8, work out14x−8y=
6
If x = 14 and y = 5, work out10x−8y=
7
If x = 10 and y = 4, work out15x−2y=
8
If x = 9 and y = 14, work out6x−3y=
9
If x = 4 and y = 2, work out7x−6y=
10
If x = 18 and y = 15, work out5x−2y=
11
If x = 6 and y = 3, work out10x−3y=
12
If x = 3 and y = 15, work out10x−13y=
13
If x = 13 and y = 6, work out9x−11y=
14
If x = 9 and y = 5, work out7x−8y=
15
If x = 12 and y = 9, work out4x−5y=
16
If x = 15 and y = 8, work out8x−3y=
17
If x = 10 and y = 9, work out7x−4y=
18
If x = 18 and y = 13, work out6x−10y=
19
If x = 14 and y = 6, work out3x−4y=
20
If x = 9 and y = 6, work out10x−9y=

What is in this set

The numbers in this set run from 2 to 18.
Every problem in it will substitute two letters.
A careful solution takes 3 written steps on average.
The mistake this set invites most often, in 100% of the problems: the two terms were added; the sign in front of the second term belongs to it.
Answers are a whole number.

Drawing 240 problems from this page produced 238 different ones, 99% — so a sheet of 20 is a new sheet almost every time.

The same skill, harder or easier

We would put this in front of a grade 7 class. That is our judgement, not a standard, and it is printed here so you can disagree with it. Everything else we put in that year.