Step by step
The question
Question: find the value of 2x + 3y when x = 1 and y = 4.
2x + 3y
x = 1, y = 4
1 Put the numbers in
We put 1 in place of x and 4 in place of y.
2x means 2 times x.
So we write a times sign.
= 2 × 1 + 3 × 4
2x = 2 × x
2 Times and divide
Times comes before plus.
Times and divide: we go from left to right.
Order: ( ) → x² √ → × ÷ → + −
same kind: left → right
2 times 1 is 2.
= 2 + 3 × 4
Times comes before plus.
3 times 4 is 12.
= 2 + 12
3 Plus and minus
2 plus 12 is 14.
= 14
Careful!
Many people go from left to right and get 20.
But times and divide come before plus and minus.
Careful: not 2 × 1 + 3 × 4 = 20 ✗
So 2x + 3y is 14 when x = 1 and y = 4.
Let's look back.
First: put the numbers in.
Then: times and divide.
Last: plus and minus.
Answer
= 14