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**AVERAGE
SPEED**

Means,If an object travels D1, D2, D3, …… Dn distances, with speeds
S1, S2, S3, …… Sn in T1,T2,T3 …… Tn times respectively, then
Average Speed

**SOME IMPORTANT FORMULAE - from
Test's point of view**

**1)**

If an object travels a distance D1 and D2 at a speed of S1 and S2
Miles per Hour, respectively, in time T1 and T2 then the total time
taken 'T' is given by:
**The total distance covered 'D' is given by:**
**2)**

If a certain distance D, from point X to point Y is traveled at 'a'
km/hr and the same distance is covered i.e. from Y to X at 'b'
km/hr, then the average speed during the whole journey can be
calculated as:

**Also, if T1 and T2 are the times taken to travel from X to
Y and from Y to X respectively, the distance D from X to Y can be
calculated as:**
**3)**

While a certain distance 'D' is covered, if A man changes his speed
in the ratio X : Y, then the ratio of time taken becomes Y :
X.

**4)**

If an object travels a distance D from X to Y with Speed 'a' in
time T1 and travels back from Y to X with of the
usual speed 'a', then the change in time taken to travel the same
distance can be calculated as:

; for n > m

; for m > n

*5)

IF two objects, say A and B, start at the same time in opposite
directions from two different points (P and Q) and arrive at the
opposite points in 'a' and 'b' hours respectively after having
met.

**Then the ratio of their speed is:**

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