# SDT... still struggling

##### Member

Just wanted to throw a few more of these SDT questions out there and see how people go about answering them. Having made some progress last week and then going away for a few days I have completely lost any technique that I was starting to gain!

At 65 mph, how long does it take to travel 78 miles?

At 90 mph, how long does it take to travel 15 miles?

At 152 mph, how far do you travel in 2 hours and 30 mins?

At 5 mph, how far do you travel in 2 hours and 24 mins?

Any help with any of the above would be great - obviously I can get to the answer eventually but just wanted to see peoples methods!

Cheers

#### BrigRat

##### Venerated Contributor
For the first one, I always think: T=D/S

78/65 = 1 and 13/65

13/65 = 1/5

Therefore, 1 hour and 12 minutes.

Could be wrong, but that's how I'd do it.

#### TheGeek

##### Venerated Contributor
Well at 65mph it will tak 1 hour to do the 65 leaving 13miles, 13 goes into 65 5 times, 60/5 =12 so 72 minutes.

Geek

#### BrigRat

##### Venerated Contributor
Third one is: D=ST

152 x 2.5

152 x 5 = 760

760/2 = 380 miles.

That's how I do it at least, basically just simplify my numbers and use my fingers to count when doing big sums. Can do it with that method in about a minute, but I'm not sure if that's fast enough.

For the last question, I made the 24 minutes a fraction (2/5) and then a decimal (0.4) then added it with the 2 and times by 5 - took slightly less than a minute.

#### Mr D

##### Venerated Contributor
Use S-D-T triangle,

1- 1 :12 divide the distance/speed 78/65=1.2,dont forget the answer is in decimal form so change the .2 to seconds ie 60x 0.2=12

2-10 mins-can do this the same way but with those figures,you can see that 90 is a multiple of 15 ie-90/15=6,so thats a 6th of an hour so 10mins

3-quite straight forward that one S xT 152 x 2.5 = 380 miles

4-12 miles,as above realey, 24mins is .4 of an hour so its 2.4 x 5 =12

#### Eyebrows

##### Valuable Contributor
I've really improved with these over the past week or two.
1. 1 hr 12 mins.... 75-68= 13..... 13 is 1/5 of 68. 1/5 of an hour is 12 minutes. so the answer is 1:12
2. 10 mins..... 15 is 1/6 of 90. 1/6 of an hour is 10 minutes
3. 380 miles..... 152 x 2.5
4. 12 miles...... 2 hours= 10 miles....... 24 minutes= 2/5.......2/5 of 5= 2.....so 12 miles

##### Venerated Contributor
The only thing I could say is make sure you break the questions down into parts instead of trying to calculate it all in one go.

1. You know that you'll travel 65 miles in one hour so take that as your first step. That then leaves you with a leftover 13 miles to travel in the remaining time, you can just use a basic SDT equation now. T = D/S = 13/65 = 0.2. Bear in mind that is 0.2 of 1 hour which will be 12 minutes so 1 hour 12 minutes.

2. T = D/S = 15/90 = 1/6. Therefore 60/6 = 10 minutes.

3. You know you will go 152 miles in one hour, so in 2 you will travel 204. As the remaining time is half of one hour then you'll only be able to travel half of this distance you would in a full hour. 152/2 = 76. So 204 + 76 = 280 miles.

4. You travel 5 miles in one hour, in 2 you will travel 10. For the remaining 24 minutes this is 2/5 of an hour. 2/5 of 5 = 2. 10 + 2 = 12 miles.

#### JohnDoe

##### Venerated Contributor
We must keep doing these. I find when I leave them for a bit I get slightly slower when doing them, naturally. Maybe we can dig up the thread we made the other day and keep posting examples if you guys are keen?

• Eyebrows

#### JohnDoe

##### Venerated Contributor
Ok Dug you are in, I will post some questions in the old thread and we can go from there. Maybe we should try just giving the answer initially and if someone struggles we can then show our working.