A started a business with Tk. 4000 and is joined afterwards by B with Tk. 6000. After how many months did B join if the profits at the end of the year are divided equally?

Question: A started a business with Tk. 4000 and is joined afterwards by B with Tk. 6000. After how many months did B join if the profits at the end of the year are divided equally?

Solution:
Let,
B joined after = x months

Then,
4000 × 12 = 6000 × (12 - x)
⇒ 48000 = 72000 - 6000x
⇒ 480 = 720 - 60x
⇒ 60x = 240
∴ x = 4

∴ B joined after 4 months.