#include <iostream>
#include <vector>
#include <algorithm>

using namespace std;

const int MAX_N = 200;
const int MOD = 1e9 + 7;

struct mint {
    int n;
    mint(int n_ = 0) : n(n_) {}
};

mint operator+(mint a, mint b) { a.n += b.n; if (a.n >= MOD) a.n -= MOD; return a; }
mint operator-(mint a, mint b) { a.n -= b.n; if (a.n < 0) a.n += MOD; return a; }
mint operator*(mint a, mint b) { return (long long)a.n * b.n % MOD; }
mint &operator+=(mint &a, mint b) { return a = a + b; }
mint &operator-=(mint &a, mint b) { return a = a - b; }
mint &operator*=(mint &a, mint b) { return a = a * b; }

mint dp[MAX_N+1][MAX_N*2][MAX_N+1];
mint I[1000];

mint modpow(mint a, int b) {
  mint res = 1;
  while (b > 0) {
    if (b & 1) res *= a;
    a *= a;
    b >>= 1;
  }
  return res;
}

mint modinv(mint a) {
  return modpow(a, MOD - 2);
}

mint f(mint *a, mint l, mint r) {
  mint res = 0;
  mint L = 1;
  mint R = 1;
  for (int i = 0; i <= MAX_N; i++) {
    L *= l;
    R *= r;
    res += a[i] * (R - L) * I[i + 1];
  }
  return res;
}

int main() {
  I[1] = 1;
  for (int i = 2; i < 1000; i++) {
    I[i] = I[MOD % i] * (MOD - MOD / i);
  }
  int N;
  cin >> N;
  vector<int> A(N), B(N), C;
  for (int i = 0; i < N; i++) {
    cin >> A[i] >> B[i];
    C.push_back(A[i]);
    C.push_back(B[i]);
  }
  sort(C.begin(), C.end());
  C.erase(unique(C.begin(), C.end()), C.end());
  int M = C.size() - 1;
  {
    int l = lower_bound(C.begin(), C.end(), A[0]) - C.begin();
    int r = lower_bound(C.begin(), C.end(), B[0]) - C.begin();
    for (int i = l; i < r; i++) {
      dp[0][i][0] = modinv(B[0] - A[0]);
    }
  }
  for (int i = 1; i < N; i++) {
    int l = lower_bound(C.begin(), C.end(), A[i]) - C.begin();
    int r = lower_bound(C.begin(), C.end(), B[i]) - C.begin();
    mint s = 0;
    for (int j = 0; j < M; j++) {
      dp[i][j][0] += s;
      dp[i][j][0] -= f(dp[i - 1][j], 0, C[j]);
      for (int k = 0; k < MAX_N; k++) {
        dp[i][j][k + 1] += dp[i - 1][j][k] * I[k + 1];
      }
      s += f(dp[i - 1][j], C[j], C[j + 1]);
    }
    if (i % 2 == 0) {
      for (int j = 0; j < M; j++) {
        for (int k = 0; k <= MAX_N; k++) {
          dp[i][j][k] *= MOD - 1;
        }
        dp[i][j][0] += s;
      }
    }
    mint v = modinv(B[i] - A[i]);
    for (int j = 0; j < M; j++) {
      for (int k = 0; k <= MAX_N; k++) {
        if (l <= j && j < r) {
          dp[i][j][k] *= v;
        } else {
          dp[i][j][k] = 0;
        }
      }
    }
  }
  mint ans = 0;
  for (int i = 0; i < M; i++) {
    ans += f(dp[N - 1][i], C[i], C[i + 1]);
  }
  cout << ans.n << '\n';
}