## Solve Lesson 9 Page 26 Math 10 – Kite >

Topic

Ha, Chau, Lien and Ngan went to buy milk tea together. All four of you have a total of 185 thousand VND. Four friends buy four cups of milk tea for 35,000 VND a cup. You order more pearls for milk tea. A portion of black pearls costs 5 thousand dong, a portion of white pearls costs 10 thousand dong. Let x, y be the number of black and white pearls, respectively, that the four of you plan to buy more.

a) Write a first-order inequality for two unknowns x, y to show how much you can afford to pay for the black and white pearls.

b) Show an integer solution of the inequality.

Detailed explanation

a) The amount to buy four cups of milk tea is: 35.4 = 140 (thousand dong).

The amount when adding x part of black pearl is: 5x (thousand dong).

The amount when adding y portion of white pearls is: 10y (thousand dong).

The total amount that the four of you have to pay for 4 cups of milk tea and extra pearls is:

5x + 10y + 140 (thousand dong).

Since the four of you have a total of 185 thousand dong, 5x + 10y + 140 185

⇔ x + 2y 9

So the first-order inequality of two unknowns x, y to represent the amount you can afford to pay for the black and white pearls is x + 2y ≤ 9.

b) The pair (x;y)=(1; 1) is an integer solution of the given inequality because:

1 + 2.1=3 ≤ 9.