Question 1 - Page 171 - Acitvity and Question - Page 171 - Chapter 7 Class 8 - Proportional Reasoning-1(Ganita Prakash)

Transcript

Question 1 - Page 171 Puneeth’s father went from Lucknow to Kanpur in 2 hours by riding his motorcycle at a speed of 50 km/h. If he drives at 75 km/h, how long will it take him to reach Kanpur? Puneeth’s father drives a motorcycle from Lucknow to Kanpur. Case 1: He drives at 50 km/h and it takes 2 hours. Case 2: He speeds up to 75 km/h. How long will it take now? Let’s solve this as Proportion 50 : 2 :: 75 : Time Converting into fraction 50/2=75/𝑇𝑖𝑚𝑒 Time =(𝟕𝟓 × 𝟐)/𝟓𝟎 Time =(3 × 2)/2 Time = 3 hours So, this means that if you drive a motorcycle for higher speed – 75 km/hr, it will take longer time But, it is not possible Hence we cannot use Proportion for this The Explanation: In a normal (direct) proportion, if one thing increases, the other increases too (e.g., if you buy more chocolates, you pay more money). But think about speed: If you drive faster, do you take more time or less time to reach your destination? You take less time! This is called Inverse Proportion. Speed goes UP ↑ Time goes DOWN ↓ Because they move in opposite directions, you cannot use the standard "Rule of Three" (Direct Proportion) formula. If you used the formula 50:2 :: 75:x, you would get an answer of 3 hours}, which makes no sense (driving faster shouldn't take longer!).