A mouse is running at the speed of 15 m/min. After 12 min a cat saw him and started running to catch the mouse at the speed of 16 m/min. How much time will it take to catch the mouse if the cat can boost his speed by 1 m/min in every 5 min?
A mouse is running at the speed of 15 m/min. After 12 min a cat saw him and started running to catch the mouse at the speed of 16 m/min. How much time will it take to catch the mouse if the cat can boost his speed by 1 m/min in every 5 min? Correct Answer <span style="font-size: 12pt; line-height: 115%; font-family: Calibri, sans-serif;">40 min</span>
Distance covered by mouse in 10 min = speed of mouse × time = 15 × 12 = 180 meter
Cat needs to cover the distance of 180 meters to catch the mouse.
Relative speed of Cat and mouse for first 5 min = 16 – 15 = 1 m/min
Relative speed of Cat and mouse for next 5 min = (16 + 1) – 15 = 2 m/min
Relative speed of Cat and mouse for next 5 min = (16 + 2) – 15 = 3 m/min and so on.
So, Distance covered in first 5 min = 1 × 5 = 5 meters
Distance covered in next 5 min = 2 × 5 = 10 meters
Distance covered in next 5 min = 3 × 5 = 15 meters and so on.
Total distance to be covered = 180 meter
So, we’ll use Arithmetic progression and first term of it a = 5 m, d = 10 – 5 = 5 and Sn = 180 m
⇒ Sn = n/2 ×
⇒ 180 = n/2 ×
⇒ 360 = n ×
⇒ n2 + n – 72 = 0
⇒ (n – 9) (n + 8) = 0
⇒ n = 8 and n = – 9
Here, n = 8 shows no. of time speed changes.
∴ Total time to catch the mouse = 8 × 5 min = 40 min