Harry, Jack and David had the same number of marbles. David gave 0.6 of his marbles to Jack. Then Jack gave 0.25 of his marbles to Harry. Finally, after Jack gave 34 marbles to David, he had the same number of marbles as David. How many marbles did David have at first?
| |
Harry |
Jack |
David |
| Before |
1 u |
1 u |
1 u |
| Change 1 |
|
+ 0.6 u |
- 0.6 u |
| After 1 |
1 u |
1.6 u |
0.4 u |
| Change 2 |
+ 0.4 u |
- 0.4 u |
|
| After 2 |
1.4 u |
1.2 u |
0.4 u |
| Change 3 |
|
- 34 |
+ 34 |
| After 3 |
1.4 u |
1.2 u - 34 |
0.4 u + 34 |
Number of marbles that Jack gave to Harry
= 0.25 x 1.6 u
= 0.4 u
The number of marbles that Jack and David had in the end is the same.
1.2 u - 34 = 0.4 u + 34
1.2 u - 0.4 u = 34 + 34
0.8 u = 68
1 u = 68 ÷ 0.8 = 85
Number of marbles that David had at first
= 1 u
= 85
Answer(s): 85
