A box contains red and black marbles in the ratio 3: 5. If there are 40 more black marbles than red, how many marbles are there in total?

Let the number of red marbles = $3x$ and black marbles = $5x$ (since the ratio is 3:5).

We are given that there are 40 more black marbles than red:

$5x - 3x = 40$

$2x = 40$

$x = 20$

Number of red marbles = $3x = 60$
Number of black marbles = $5x = 100$

Total marbles = 60 + 100 = 160

✅ Answer: 160 marbles