The ratio of Robert's marbles to Sofia's marbles at first was 3 : 7. After Robert gave Sofia 100 marbles, the ratio of Robert's marbles to Sofia's marbles is 1 : 3. What was the number of marbles they had in total?
| |
Robert |
Sofia |
Total |
| Before |
3x4 =
12 u |
7x4 =
28 u
|
10x4 =
40 u |
| Change |
- 100 |
+ 100 |
|
| After |
1x10 =
10 u |
3x10 =
30 u |
4x10 =
40 u |
Number of marbles that Robert gave Sofia
= 12 u - 10 u
= 2 u
2 u = 100
1 u = 100 ÷ 2 = 50
Total number of marbles that they had
= 40 u
= 40 x 50
= 2000
Answer(s): 2000
