Math Practice Paper Question

Dear 6B

We have discussed the following question in class and let me explain why the answer $30 is wrong using the following method.


Keith bough 5 times as many toy cars as computer games for his friends. He spent a total of $455.
He spent $65 more on the toy cars than the computer games.
Each toy car cost $11 less than each computer game.
What is the cost of each computer game?


Let Toy cars be x and computer games be y

5x + y = 455
5x = 65 + y
x= y -11

5(y-11) = 65 + y
5y - 55 + 65 + y
5y - y = 65 + 55
4y = 120
y= 30


Explanation

The first sentence is already wrong.

Let toy cars means the number of toy car in this case because the equation formed is 5x + y = 455.
This is incorrect because 5 times of toy cars + number of computer games is not equal to $455.
There is no clue that suggests the total number of toy car and computer games at all.


Let say x refers to the cost of one toy car and y refers to the cost of computer game
then only x=y-11 makes sense.
5x means the cost of one toy car times 5 and to add it to the price of one computer game will never give me 455.
Similarly, 5x =65 + y will not make sense since we do not know how many sets of toy cars and computer games there are.

so remember

The key step to solve this word problem is to make comparison between one unit of computer games and one unit of toy car.