David has 70% as many buttons as Ben. If David gives away 20% of the buttons and Ben gives away 40% of his buttons, they will have 580 buttons altogether. How many buttons do the two of them have?
| |
David |
Ben |
Total |
Comparing David
and Ben at first |
7x5 =
35 u |
10x5 =
50 u |
|
| Before |
5x7 =
35 u |
5x10 =
50 u |
|
| Change |
- 1x7 =
- 7 u |
- 2x10 =
- 20 u |
|
| After |
4x7 =
28 u |
3x10 =
30 u |
580 |
70% =
70100 =
710 20% =
20100 =
15 40% =
40100 =
25 The number of buttons that David has at first is repeated. Make the number of buttons that David has the same. LCM of 7 and 5 is 35 u.
The number of buttons that Ben has at first is repeated. Make the number of buttons that Ben has the same. LCM of 10 and 5 is 50 u.
Number of buttons in the end
= 28 u + 30 u
= 58 u
58 u = 580
1 u = 580 ÷ 58 = 10
Total number of buttons that the two of them have
= 35 u + 50 u
= 85 u
= 85 x 10
= 850
Answer(s): 850
