# CBSE Class 10 Math Question Paper 2018 | Q23A

###### CBSE Solved Question Paper 4 Mark | Quadratic Equations

Question 23A: A motor boat whose speed is 18 km/hr in still water takes 1hr more to go 24 km upstream than to return downstream to the same spot. Find the speed of the stream.

## NCERT Solution to Class 10 Maths

### Explanatory Answer | CBSE Class 10 Math Paper 2018 Q23A

Still water speed of motor boat = 18 km/hr
Let the speed of stream = s km/hr

Upstream speed of boat = (18 - s) km/hr
Downstream speed of boat = (18 + s) km/hr

Time taken to travel 24 km upstream = $$frac{24}{18 - S}$ Time taken to travel 24 km downstream = $\frac{24}{18 + S}$ Time for upstream = Time for downstream + 1 hour $\frac{24}{18 - s}$ = $\frac{24}{18 + s}$ + 1 $\frac{24$18 + s$ − 24(18 − s)}{(18 − s) (18 + s)}) = 1
2 × 24 × s = 182 - s2
Or s2 + 48s - 324 = 0
s2 + 54s – 6s - 324 = 0
s = -54 or s = 6

Speed has to be positive.
∴ Speed of stream = 6 km/hr

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