#include <cstdio>
typedef long long ll;
const int MOD = 1000000007, MAX = 5020;
ll modpow(ll a, ll x) {
ll ret = 1;
a = a % MOD;
while (x) {
if (x & 1) ret = ret * a % MOD;
a = a * a % MOD;
x >>= 1;
}
return ret;
}
int success[MAX], fail[MAX], damage[MAX];
//failSum, failX는 조합의 개수를 셈
ll failSum[MAX][MAX], failX[MAX][MAX];
ll rotate(ll x) {
return x < 0 ? x + MOD : x;
}
int main() {
int n;
scanf("%d", &n);
const ll divider = modpow(1000000000, MOD-2);
for (int i = 0; i < n; i++) {
scanf("%d%d", &success[i], &damage[i]);
success[i] = success[i] * divider % MOD;
fail[i] = 1 - success[i];
if (fail[i] < 0) fail[i] += MOD;
}
ll res = 0;
ll selectRate = modpow(n, MOD-2);
for (int i = n-1; i >= 0; i--) {
//1번째로 i가 실패할 확률
failX[1][i] = (selectRate * fail[i]) % MOD;
failSum[1][i] = (failX[1][i] + failSum[1][i+1]) % MOD;
//1번째로 i가 성공할 확률
res = (res + selectRate * success[i] % MOD * damage[i] % MOD) % MOD;
}
//factorial은 (order-1)!을 저장
ll factorial = 1;
for (int order = 2; order <= n; order++) {
factorial = factorial * (order-1) % MOD;
selectRate = modpow(n-order+1, MOD-2);
for (int i = n-1; i >= 0; i--) {
ll tmp;
//order개 중 i가 실패한 것이 포함된 것 확률
tmp = rotate(failSum[order-1][0] - failX[order-1][i]) * selectRate % MOD;
tmp = tmp * fail[i] % MOD;
failX[order][i] = tmp;
//order번째로 i가 성공할 확률
tmp = factorial * rotate(failSum[order-1][0] - failX[order-1][i]) % MOD;
tmp = tmp * selectRate % MOD;
tmp = tmp * success[i] % MOD;
res = (res + tmp * damage[i] % MOD) % MOD;
}
for (int i = n-1; i >= 0; i--) {
failSum[order][i] = (fail[i] * selectRate) % MOD * failSum[order-1][i+1] % MOD;
failSum[order][i] = (failSum[order][i] + failSum[order][i+1]) % MOD;
}
}
printf("%lld\n", res);
return 0;
}
