Luis has some black and white marbles. The total mass of all his marbles is 204 g. He has 3 more white marbles than black marbles. The average mass of the black marbles is 9 g. The average mass of the white marbles is 12 g. How many marbles does Luis have altogether?
| |
Black |
White |
Total |
| Number |
1 u |
1 u + 3 |
2 u + 3 |
| Value |
9 |
12 |
|
| Total value |
9 u |
12 u + 36 |
204 |
Total mass of black marbles
= 1 u x 9
= 9 u
Total mass of white marbles
= 12(1 u + 3)
= 12 u + 36
Total mass of the marbles
= 9 u + 12 u + 36
= 21 u + 36
21 u + 36 = 204
21 u = 204 - 36
21 u = 168
1 u = 168 ÷ 21 = 8
Total number of marbles
= 2 u + 3
= 2 x 8 + 3
= 16 + 3
= 36
Answer(s): 36
