#include <iostream>
#include <vector>
#include <map>
#include <set>
#include <queue>
#include <string>
#include <iomanip>
#include <algorithm>
#include <cmath>
#include <stdio.h>
using namespace std;
#define int long long
int MOD = 1000000007;
template <typename Int, Int MOD, int N>
struct comb_util {
	std::array<Int, N + 1> fc, ifc;

	comb_util() {
		fc[0] = 1;
		for (int i = 1; i <= N; i++) fc[i] = fc[i - 1] * i % MOD;
		ifc[N] = inv(fc[N]);
		for (int i = N - 1; i >= 0; i--) ifc[i] = ifc[i + 1] * (i + 1) % MOD;
	}

	Int fact(Int n) { return fc[n]; }

	Int inv_fact(Int n) { return ifc[n]; }

	Int inv(Int n) { return pow(n, MOD - 2); }

	Int pow(Int n, Int a) {
		Int res = 1, exp = n;
		for (; a; a /= 2) {
			if (a & 1) res = res * exp % MOD;
			exp = exp * exp % MOD;
		}
		return res;
	}

	Int perm(Int n, Int r) {
		if (r < 0 || n < r)
			return 0;
		else
			return fc[n] * ifc[n - r] % MOD;
	}

	Int binom(Int n, Int r) {
		if (n < 0 || r < 0 || n < r) return 0;
		return fc[n] * ifc[r] % MOD * ifc[n - r] % MOD;
	}

	Int homo(Int n, Int r) {
		if (n < 0 || r < 0) return 0;
		return r == 0 ? 1 : binom(n + r - 1, r);
	}
};

using comb = comb_util<long long, 1000000007, 300000>;
comb cb;
void add(int &a, const int &b) {
	a += b;
	if (a >= MOD)a -= MOD;
}
signed main() {
	cin.tie(0);
	ios::sync_with_stdio(false);
	int N;
	cin >> N;
	vector<int> A(N), B(N);
	int res = 0;
	set<int> st;
	vector<int> X;
	map<int, int> mp;
	for (int i = 0; i < N; i++) {
		cin >> A[i] >> B[i];
		st.insert(A[i]);
		st.insert(B[i]);
	}
	for (auto s : st) {
		mp[s] = X.size();
		X.push_back(s);
	}
	int M = X.size();

	vector<vector<int> > C(N + 1, vector<int>(N + 1, 0));

	C[0][0] = 1;
	for (int i = 1; i <= N; i++) {
		int sum = 0;
		int b = cb.inv(i + 1);
		if (i % 2 == 1) {
			for (int j = 0; j <= i; j++) {
				add(C[i][j], (b * sum) % MOD);
				add(sum, C[i - 1][j]);
			}
		}
		else {
			for (int j = i; j >= 0; j--) {
				add(sum, C[i - 1][j]);
				add(C[i][j], (b * sum) % MOD);
			}
		}
	}
	vector<int> D(N);
	for (int i = 0; i < N; i++) {
		D[i] = 0;
		for (int j = 0; j <= N; j++) {
			add(D[i], C[i + 1][j]);
		}
		//cerr << i << " " << D[i] << endl;
	}
	vector<int> E(N);
	for (int i = 0; i < N; i++) {
		E[i] = 1;
		if (i > 0) {
			E[i] = cb.inv(D[i - 1]);
		}
		E[i] = (E[i] * D[i]) % MOD;
	}

	//cerr << (E[0] * E[1]) % MOD << endl;



	vector<vector<int> > dp(M - 1, vector<int>(N, 0));
	int l = mp[A[0]];
	int r = mp[B[0]];

	int b = cb.inv(B[0] - A[0]);
	for (int i = l; i < r; i++) {
		dp[i][0] = b * (X[i + 1] - X[i]) % MOD;
	}
	int inv2 = (MOD + 1) / 2;
	for (int i = 1; i < N; i++) {
		vector<vector<int> > ndp(M - 1, vector<int>(N, 0));
		l = mp[A[i]];
		r = mp[B[i]];
		b = cb.inv(B[i] - A[i]);
		if (i % 2 == 1) {
			int sum = 0;
			for (int j = 0; j < M - 1; j++) {
				if (l <= j && j < r) {
					int tt = ((X[j + 1] - X[j]) * b) % MOD;
					add(ndp[j][0], tt * sum % MOD);
					for (int k = 0; k < N - 1; k++) {
						add(ndp[j][k + 1], ((tt * dp[j][k] % MOD) * E[k]) % MOD);
					}
				}
				for (int k = 0; k < N; k++) {
					add(sum, dp[j][k]);
				}
			}
		}
		else {
			int sum = 0;
			for (int j = M - 2; j >= 0; j--) {
				if (l <= j && j < r) {
					int tt = ((X[j + 1] - X[j]) * b) % MOD;
					add(ndp[j][0], tt * sum % MOD);
					for (int k = 0; k < N - 1; k++) {
						add(ndp[j][k + 1], ((tt * dp[j][k] % MOD) * E[k]) % MOD);
					}
				}
				for (int k = 0; k < N; k++) {
					add(sum, dp[j][k]);
				}
			}
		}
		swap(dp, ndp);
	}

	for (int i = 0; i < M - 1; i++) {
		for (int j = 0; j < N; j++) {
			add(res, dp[i][j]);
		}
	}

	cout << res << endl;
}