Question

Antonio has a total of 55 marbles. He has 15 green marbles and 12 red marbles. The rest of the marbles are blue. How many blue marbles does he have?

A student solves this problem by writing an equation. Which strategy could help check the student’s answer?

Answer 1

total = green marbles + red marbles + blue marbles
55 = 15 + 12 + blue marbles
55 = 27 + blue marbles
55 - 27 = blue marbles
28 = blue marbles

Answer 2

Answer:

Antonio has $28$ blue marbles

Step-by-step explanation:

Let

x------> the number of green marbles

y------> the number of red marbles

z------> the number of blue marbles

we know that

$x+y+z=55$ -----> equation A

$x=15$ ----> equation B

$y=12$ ----> equation C

Substitute equation B and equation C in equation A and solve for z

$15+12+z=55$

$27+z=55$

Subtract $27$ both sides

$27+z-27=55-27$

$z=28$