Here’s and example of a **SMART MATH** problem for **TIME SPEED DISTANCE.**

**Problem**

**Problem**

Mira rowed upstream in a stream flowing at the rate of 1.5 km/hr to a certain point and then rowed back stopping 2 kms short of the place where she originally started. If the rowing time was 2 hours 20 minutes and her uniform speed in still water was 4.5 km/hr, how far upstream did she go?

- 4.25 kms
- 5.33 kms
- 6.50 kms
- 7.00 kms
- 8.75 kms

**The Usual Method**

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Speed of Mira in still water = 4.5 km/hr.

Speed of stream = 1.5 km/hr

Hence upstream travel speed = 4.5 – 1.5 = 3 km/hr

And downstream travel speed = 4.5 + 1.5 = 6 km/hr

Let the distance traveled upstream = *x* kms.

Time taken to travel upstream = hours

Time taken to travel downstream = hours

Total time taken = + = 2 hours 20 minutes

5.33 kms

**(Ans: 2)**

*Estimated Time to arrive at the answer = 75 seconds.*

**Using Technique**

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Since the upstream travel speed = 4.5 – 1.5 = 3 km/hr and downstream travel speed = 4.5 + 1.5 = 6 km/hr (both being integers), but total travel time = hours (being a fraction with denominator as 3), the answer should also be a fraction with denominator as 3. The only answer satisfying this condition is 5.33 kms.

**(Ans: 2)**

*Estimated Time to arrive at the answer = 5 seconds.*

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