John had twice as many marbles as Carl. After Carl lost 10 marbles and John bought 10 marbles, John had 4 times as many marbles as Carl. How many marbles did John and Carl have altogether at first?
| |
John |
Carl |
Total |
| Before |
2x5 =
10 u |
1x5 =
5 u |
3x5 =
15 u |
| Change |
+ 10 |
- 10 |
|
| After |
4x3 =
12 u |
1x3 =
3 u |
5x3 =
15 u |
The number of marbles that Carl lost and bought is the same. So, the total number of marbles remains unchanged. Make the total number of marbles the same. LCM of 3 and 5 is 15.
Number of marbles that John bought
= 12 u - 10 u
= 2 u
2 u = 10
1 u = 10 ÷ 2 = 5
Number of cards that they had altogether at first
= 15 u
= 15 x 5
= 75
Answer(s): 75
