Mathematics is one of the difficult subjects, many students have difficulty in learning mathematics and have a bad impact on students' attitudes and learning motivation. This is caused by the lack of competence that students have in understanding mathematical concepts. This study aims to determine the effect of mathematical disposition on the ability to understand mathematical concepts. The research method is quantitative research with correlational survey method with simple regression analysis. The target population, namely all students of the Malahayati Islamic Middle School. The population reached was only the VIII grade students of Malahayati Islamic Junior High School. The research sample amounted to 26 respondents with a simple random sampling technique. The research instrument was a mathematical disposition questionnaire and a question about the ability to understand mathematical concepts. The technique of data analysis was done by correlation test and simple regression test. Overall, it can be said that there is a positive and insignificant effect on students' ability to understand mathematical concepts.

The purpose of this study is to measure the economic value in Rawapening. This study is expected to be able to see how far the role of nature tourism is seen as an environmentally sound tourist attractions. Because the benefits of natural attractions usually have a variety of natural resources such as biodiversity, benefit directly, and indirectly related to important ecological functions that are not only considered as a tourist attraction.This study was used primary data. The primary data obtained from field surveys to the perpetrator who was visiting tourist Rawapening. The analytical method used two methods. There are travel cost method and contingent valuation method.The study was found significant factors the determinant of the probability of individuals to be willing to pay a certain nominal value for environmental quality improvement are nominal amount bid, income, and education. Then, the determinant of the number of visits are an experience to visit, travel costs, income, age, and perception. The economic value of ecotourism was estimated at Rp 7,41 billion for consumer surplus and Rp 1,65 billion for total benefit per year. This implies that the significant economic value of nature based tourism will be lost from any large scale development by degrading natural environment.

The study of the effects of exchange rate volatility has still attracted the attention among economist, especially international economist. Because, if the exchange rate is unpredictable, it makes uncertainty about the profits to be gained, so this conditions may diminish the gain from international trade. In addition, some empirical literature provides various findings, where the exchange rate volatility has a positive effect on exports and can also negatively effect on exports. This paper wants to provide empirical evidence on both of these. It uses panel data involving five ASEAN countries with a period of 2000 – 2016. We also apply some analysis in panel data, such as the pooled least squares method, the fixed effect method, and the random effect method. The findings show that the exchange rate volatility has negative impact on exports. This paper suggests that each of central bank should pursue sustainable and stable exchange rate policy measures to promote greater exchange rate stability that would help to enhance the real exports of the economy.

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