In a 150 m race, A gives B a start of 20 m. When A finishes the 150 m, what distance has B covered?

Introduction / Context:
A start of s meters in a race of L meters means the slower runner B only needs to cover L - s meters in the time A covers L meters. The question asks B's distance at the moment A finishes.

Given Data / Assumptions:

• Race length L = 150 m; start to B = 20 m.
• So B's required distance = L - s = 150 - 20 = 130 m.

Concept / Approach:
By definition, at A's finish, B has completed exactly his reduced race distance if they tie under the given start. If no further speed data are given, the distance for B at A's finish time is 130 m.

Step-by-Step Solution:
Compute B's race distance: 150 - 20 = 130 m Therefore, at A's finish, B has covered 130 m.

Verification / Alternative check:
This is a direct interpretation of a start. If A and B had equal effective completion times with that head start, B's course length is shortened by the start amount.

Why Other Options Are Wrong:
100, 170, or 160 m conflict with the definition of a 20 m start on a 150 m race when no other timing differences are specified.

Common Pitfalls:
Confusing a start with a handicap on time; assuming a speed ratio without data; misreading that 20 m start reduces B's distance, not A's.

Final Answer:
130 m