Some marbles are to be packed in four boxes, A, B, C and D, in the proportion of 6 : 3 : 7 : 5. If box B has 400 less marbles than box D, then how many marbles are there in total in all the boxes?

Correct option is C

Given:

The marbles are packed in boxes A, B, C, and D in the ratio 6:3:7:5.

Box B has 400 less marbles than box D.

Solution:

Let the number of marbles in boxes A, B, C, and D be represented as 6x, 3x, 7x, and 5x, respectively.

From the given condition:

5x - 3x = 400 
2x = 400

x = 200 

Box A: 6x = 6 $$\times 200 = 1200$$​​

Box B: 3x = 3$$\times 200 = 600$$​​

Box C: 7x = 7 $$\times 200 = 1400$$​​

Box D: 5x = $$5 \times 200 = 1000$$​​

Total number of marbles:
1200 + 600 + 1400 + 1000 = 4200 

There are 4200 marbles in total.