You should check the cutoff score rather than JEE Advanced marks. Here is the IIT Mandi cutoff for 2021.
Branch | IIT Mandi Cutoff 2021 |
Civil Engineering | 8862-11699 |
Computer Science & Engineering | 1975-3041 |
Data Science and Engineering | 2931-4020 |
Electrical Engineering | 3969-6660 |
Engineering Physics | 6861-9931 |
Mechanical Engineering | 5031-9114 |
IIT Guwahati cutoff 2021 for various courses is as follows.
Branch | IIT Guwahati Cutoff 2021 |
Biosciences & Bioengineering | 7055-8954 |
Chemical Engineering | 4063-5725 |
Chemical Science and Technology | 5418-7832 |
Civil Engineering | 5797-7545 |
Computer Science and Engineering | 439-600 |
Data Science and Artificial Intelligence | 716-954 |
From the cutoff score, you can get a better idea about your chances of getting admission.
There is a fair chance that you will get admission at IIT Mandi and IIT Guwahati with 259 marks in JEE Advanced.
But it also depends on the rank you scored in JEE Advanced as one can't predict your rank and whether you get your desired branch or not. But, and if you could have scored 250 in that paper, you could have been easily under the top 500.
So it’s all relative to paper and going by the trends of the last few years, a score of 250 will be enough to get a decent branch at these two institutes. You should go through the official website of the institute to get an idea about the required cutoff.