# A math question

1. Jan 15, 2010

### heraclius

A student normally needs 15 seconds for a 100m sprint. One day favorable wind conditionshelp her to increase her speed by 2km//h.
What is her time now?

A) aprx. 13,8 sec.
B) aprx. 13,6 sec.
C) aprx. 13 sec.
D) aprx. 14,2 sec.

Could you explain why ?

2. Jan 15, 2010

### rochfor1

What is her normal speed?

3. Jan 15, 2010

### Mensanator

Her speed, in m/sec is 100 m in 15 sec or 6.67 m/sec.

First, convert that to km/hr.

100 m is 0.1 km and there are 3600 sec in an hr.

So, her speed in km/hr is 0.1 km/(15/3600 hr) which is 24 km/hr.

Now, add the increase due to the wind: 24 km/hr + 2 Km/hr = 26 km/hr

That's 26000 m in 3600 sec. Or 7.22 m/sec.

How long does it take to run 100m at the rate of 7.22 m/sec?

100 m / (7.22 m/sec) = ~13.8 sec, so the answer is A).

4. Jan 16, 2010

### heraclius

Thank you very much!

5. Jan 16, 2010

### Staff: Mentor

It is against the policy in this forum to provide complete answers to posters' questions.