Lena has 2 boxes of buttons A and B. In total are 1.200 buttons. She move 360 buttons from box A to B. There are now 3 times as many buttons in box B than box A. Homany buttons were in box A at the start?

660

Step-by-step explanation:

Let A = number of buttons in Box A

and B = number of buttons in Box B

We have two conditions:

(1) A + B = 1200

(2) B + 360 = 3 (A - 360) Remove parentheses

B + 360 = 3A - 1080 Subtract 360 from each side

(3) B = 3A - 1440 Substitute (3) into (1)

A + 3A - 1440 = 1200 Combine like terms

4A - 1440 = 1200 Add 1440 to each side

4A = 2640 Divide each side by 4

A = 660