A 3-digit number 4a3 is added to another 3-digit number 984 to give a 4-digit number 13b7, which is divisible by 11. Then, (a +b) = ?
10
11
12
15
Explanation:
4 a 3 |
9 8 4 } ==> a + 8 = b ==> b - a = 8
13 b 7 |
Also, 13b7 is divisible by 11 $\Rightarrow$ (7 + 3) - (b + 1) = (9 - b)
$\Rightarrow$ (9 - b) = 0
$\Rightarrow$ b = 9
$\therefore$ b= 9 and a= 1 $\Rightarrow$ (a + b) = 10.