Ethan has a total of 38 of yellow and black pencils.
13 of the yellow pencils and half of the black pencils are new. How many of his black pencils are new if he has a total of 15 new pencils?
| |
Yellow pencils |
Black pencils |
Total |
| Total |
3 u |
2 p |
38 |
| New |
1 u |
1 p |
15 |
| Old |
2 u |
1 p |
23 |
Number of old pencils
= 38 - 15
= 23
1 u + 1 p = 15 --- (1)
2 u + 1 p = 23 --- (2)
(2) - (1)
(2 u + 1 p) - (1 u + 1 p) = 23 - 15
2 u - 1 u = 8
1 u = 8
1 u = 8 ÷ 1 = 8
Number of new black pencils
= 15 - 1 u
= 15 - 8
= 7
Answer(s): 7
