3characteristic of a good math explanation

1) Show all the steps: do not skip steps or assume that the other part knows what you did, you have to show whay you did.. 2) Justifiy the steps: name the rules or theorems that back up each step; you have to show why you did what you did.. 3) Verify the result: show that the answer is coherent with the information given. I like to add a reflection on the problem: what it shows, what I leaned, how these results help to fix the kwnoledges,etc.

Cost price of the burger = $4.15

Step-by-step explanation:

Given data:

3 burgers were ordered

3 medium fries were ordered

Total order cost 17.55

Let the price of the burger be X

Let the price of the medium fries be Y

Equation for the total sale will be 3X + 3Y = 17.55 (equation 1)

from this statement 'The price of a burger is .75 more than two times the price of medium fries.'

X - 2Y = 0.75 (equation 2)

There are now two equations and two unknowns, a simultaneous equation is solved to find the cost of the  burger.

Many methods can be used to solve these equations but in this case substitution will be used

From equation 2

X = 0.75 + 2Y (equation 3)

Substituting equation 3 into equation 1

3(0.75 + 2Y) + 3Y = 17.55

2.25 + 6Y + 3Y = 17.55

6Y + 3Y = 17.55-2.25

9Y = 15.3

Y = 1.7

Substituting Y into equation 3

X = 0.75 + 2Y

X = 0.75 + 2(1.7)

X = 0.75 + 3.4

X = 4.15

Therefore the cost price of the burger is $4.15